diff --git a/test/src/commonTest/kotlin/AggregationTests.kt b/test/src/commonTest/kotlin/AggregationTests.kt
--- a/test/src/commonTest/kotlin/AggregationTests.kt
+++ b/test/src/commonTest/kotlin/AggregationTests.kt
@@ -78,4 +78,22 @@
 
 		check(Song(creationDate = 12, editionDate = 1) in anomalies.find().toList())
 	}
+
+	test("Update with a condition") {
+		songs().insertOne(Song(creationDate = 0, editionDate = 1))
+		songs().insertOne(Song(creationDate = 1, editionDate = 1))
+		songs().insertOne(Song(creationDate = 2, editionDate = 3))
+
+		songs().updateManyWithPipeline {
+			set {
+				Song::creationDate set cond(
+					of(Song::editionDate) gt of(Song::creationDate),
+					of(12),
+					of(11)
+				)
+			}
+		}
+
+		check(Song(creationDate = 12, editionDate = 3) in songs().find().toList())
+	}
 })
diff --git a/dsl/src/commonMain/kotlin/aggregation/ValueDsl.kt b/dsl/src/commonMain/kotlin/aggregation/ValueDsl.kt
--- a/dsl/src/commonMain/kotlin/aggregation/ValueDsl.kt
+++ b/dsl/src/commonMain/kotlin/aggregation/ValueDsl.kt
@@ -21,6 +21,7 @@
 import opensavvy.ktmongo.dsl.KtMongoDsl
 import opensavvy.ktmongo.dsl.LowLevelApi
 import opensavvy.ktmongo.dsl.aggregation.operators.ComparisonValueOperators
+import opensavvy.ktmongo.dsl.aggregation.operators.ConditionalOperators
 import opensavvy.ktmongo.dsl.aggregation.operators.ValueOperators
 import opensavvy.ktmongo.dsl.expr.FilterOperators
 import opensavvy.ktmongo.dsl.path.Field
@@ -94,7 +95,8 @@
  */
 @KtMongoDsl
 interface ValueDsl : ValueOperators,
-	ComparisonValueOperators {
+	ComparisonValueOperators,
+	ConditionalOperators {
 
 	/**
 	 * Refers to a [field] within an [aggregation value][ValueDsl].
diff --git a/dsl/src/commonMain/kotlin/expr/UpdateOperators.kt b/dsl/src/commonMain/kotlin/expr/UpdateOperators.kt
--- a/dsl/src/commonMain/kotlin/expr/UpdateOperators.kt
+++ b/dsl/src/commonMain/kotlin/expr/UpdateOperators.kt
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2024, OpenSavvy and contributors.
+ * Copyright (c) 2024-2025, OpenSavvy and contributors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -48,7 +48,7 @@
  * ### Operators
  *
  * On regular fields:
- * - [`$inc`][inc]
+ * - [`$inc`][plusAssign]
  * - [`$rename`][renameTo]
  * - [`$set`][set]
  * - [`$setOnInsert`][UpsertOperators.setOnInsert] (only for [upserts][UpsertOperators])
@@ -130,6 +130,134 @@
 		this.field.set(value)
 	}
 
+	/**
+	 * Replaces the value of a field with the specified [value], if [condition] is `true`.
+	 *
+	 * If [condition] is `false`, this operator does nothing.
+	 *
+	 * ### Example
+	 *
+	 * ```kotlin
+	 * class User(
+	 *     val name: String?,
+	 *     val age: Int,
+	 * )
+	 *
+	 * collection.filter {
+	 *     User::name eq "foo"
+	 * }.updateMany {
+	 *     User::age.setIf(someComplexOperation, 18)
+	 * }
+	 * ```
+	 *
+	 * ### External resources
+	 *
+	 * - [Official documentation](https://www.mongodb.com/docs/manual/reference/operator/update/set/)
+	 *
+	 * @see UpsertOperators.setOnInsert Only set if a new document is created.
+	 */
+	@Suppress("INVISIBLE_REFERENCE")
+	@KtMongoDsl
+	fun <@kotlin.internal.OnlyInputTypes V> Field<T, V>.setIf(condition: Boolean, value: V) {
+		if (condition)
+			this set value
+	}
+
+	/**
+	 * Replaces the value of a field with the specified [value], if [condition] is `true`.
+	 *
+	 * If [condition] is `false`, this operator does nothing.
+	 *
+	 * ### Example
+	 *
+	 * ```kotlin
+	 * class User(
+	 *     val name: String?,
+	 *     val age: Int,
+	 * )
+	 *
+	 * collection.filter {
+	 *     User::name eq "foo"
+	 * }.updateMany {
+	 *     User::age.setIf(someComplexOperation, 18)
+	 * }
+	 * ```
+	 *
+	 * ### External resources
+	 *
+	 * - [Official documentation](https://www.mongodb.com/docs/manual/reference/operator/update/set/)
+	 *
+	 * @see UpsertOperators.setOnInsert Only set if a new document is created.
+	 */
+	@Suppress("INVISIBLE_REFERENCE")
+	@KtMongoDsl
+	fun <@kotlin.internal.OnlyInputTypes V> KProperty1<T, V>.setIf(condition: Boolean, value: V) =
+		this.field.setIf(condition, value)
+
+	/**
+	 * Replaces the value of a field with the specified [value], if [condition] is `false`.
+	 *
+	 * If [condition] is `true`, this operator does nothing.
+	 *
+	 * ### Example
+	 *
+	 * ```kotlin
+	 * class User(
+	 *     val name: String?,
+	 *     val age: Int,
+	 * )
+	 *
+	 * collection.filter {
+	 *     User::name eq "foo"
+	 * }.updateMany {
+	 *     User::age.setUnless(someComplexOperation, 18)
+	 * }
+	 * ```
+	 *
+	 * ### External resources
+	 *
+	 * - [Official documentation](https://www.mongodb.com/docs/manual/reference/operator/update/set/)
+	 *
+	 * @see UpsertOperators.setOnInsert Only set if a new document is created.
+	 */
+	@Suppress("INVISIBLE_REFERENCE")
+	@KtMongoDsl
+	fun <@kotlin.internal.OnlyInputTypes V> Field<T, V>.setUnless(condition: Boolean, value: V) {
+		if (!condition)
+			this set value
+	}
+
+	/**
+	 * Replaces the value of a field with the specified [value], if [condition] is `false`.
+	 *
+	 * If [condition] is `true`, this operator does nothing.
+	 *
+	 * ### Example
+	 *
+	 * ```kotlin
+	 * class User(
+	 *     val name: String?,
+	 *     val age: Int,
+	 * )
+	 *
+	 * collection.filter {
+	 *     User::name eq "foo"
+	 * }.updateMany {
+	 *     User::age.setUnless(someComplexOperation, 18)
+	 * }
+	 * ```
+	 *
+	 * ### External resources
+	 *
+	 * - [Official documentation](https://www.mongodb.com/docs/manual/reference/operator/update/set/)
+	 *
+	 * @see UpsertOperators.setOnInsert Only set if a new document is created.
+	 */
+	@Suppress("INVISIBLE_REFERENCE")
+	@KtMongoDsl
+	fun <@kotlin.internal.OnlyInputTypes V> KProperty1<T, V>.setUnless(condition: Boolean, value: V) =
+		this.field.setUnless(condition, value)
+
 	// endregion
 	// region $inc
 
@@ -198,6 +326,72 @@
 	infix fun <@kotlin.internal.OnlyInputTypes V : Number> KProperty1<T, V>.inc(amount: V) {
 		this.field.inc(amount)
 	}
+
+	/**
+	 * Increments a field by the specified [amount].
+	 *
+	 * [amount] may be negative, in which case the field is decremented.
+	 *
+	 * If the field doesn't exist (either the document doesn't have it, or the operation is an upsert and a new document is created),
+	 * the field is created with an initial value of [amount].
+	 *
+	 * Use of this operator with a field with a `null` value will generate an error.
+	 *
+	 * ### Example
+	 *
+	 * ```kotlin
+	 * class User(
+	 *     val name: String,
+	 *     val age: Int,
+	 * )
+	 *
+	 * // It's the new year!
+	 * collection.updateMany {
+	 *     User::age += 1
+	 * }
+	 * ```
+	 *
+	 * ### External resources
+	 *
+	 * - [Official documentation](https://www.mongodb.com/docs/manual/reference/operator/update/inc/)
+	 */
+	@Suppress("INVISIBLE_REFERENCE")
+	@KtMongoDsl
+	operator fun <@kotlin.internal.OnlyInputTypes V : Number> Field<T, V>.plusAssign(amount: V): Unit =
+		this.inc(amount)
+
+	/**
+	 * Increments a field by the specified [amount].
+	 *
+	 * [amount] may be negative, in which case the field is decremented.
+	 *
+	 * If the field doesn't exist (either the document doesn't have it, or the operation is an upsert and a new document is created),
+	 * the field is created with an initial value of [amount].
+	 *
+	 * Use of this operator with a field with a `null` value will generate an error.
+	 *
+	 * ### Example
+	 *
+	 * ```kotlin
+	 * class User(
+	 *     val name: String,
+	 *     val age: Int,
+	 * )
+	 *
+	 * // It's the new year!
+	 * collection.updateMany {
+	 *     User::age += 1
+	 * }
+	 * ```
+	 *
+	 * ### External resources
+	 *
+	 * - [Official documentation](https://www.mongodb.com/docs/manual/reference/operator/update/inc/)
+	 */
+	@Suppress("INVISIBLE_REFERENCE")
+	@KtMongoDsl
+	operator fun <@kotlin.internal.OnlyInputTypes V : Number> KProperty1<T, V>.plusAssign(amount: V): Unit =
+		this.field.plusAssign(amount)
 
 	// endregion
 	// region $unset
diff --git a/dsl/src/commonTest/kotlin/aggregation/ValueTest.kt b/dsl/src/commonTest/kotlin/aggregation/ValueTest.kt
--- a/dsl/src/commonTest/kotlin/aggregation/ValueTest.kt
+++ b/dsl/src/commonTest/kotlin/aggregation/ValueTest.kt
@@ -23,6 +23,7 @@
 import opensavvy.prepared.runner.kotest.PreparedSpec
 
 const val literal = "\$literal"
+const val cond = "\$cond"
 
 @LowLevelApi
 class ValueTest : PreparedSpec({
diff --git a/dsl/src/commonMain/kotlin/aggregation/operators/ConditionalOperators.kt b/dsl/src/commonMain/kotlin/aggregation/operators/ConditionalOperators.kt
new file mode 100644
--- /dev/null
+++ b/dsl/src/commonMain/kotlin/aggregation/operators/ConditionalOperators.kt
@@ -0,0 +1,98 @@
+/*
+ * Copyright (c) 2025, OpenSavvy and contributors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package opensavvy.ktmongo.dsl.aggregation.operators
+
+import opensavvy.ktmongo.bson.BsonContext
+import opensavvy.ktmongo.bson.BsonValueWriter
+import opensavvy.ktmongo.dsl.KtMongoDsl
+import opensavvy.ktmongo.dsl.LowLevelApi
+import opensavvy.ktmongo.dsl.aggregation.AbstractValue
+import opensavvy.ktmongo.dsl.aggregation.Value
+import opensavvy.ktmongo.dsl.aggregation.ValueDsl
+
+/**
+ * Operators to conditionally create a value.
+ *
+ * To learn more about aggregation operators, view [ValueDsl].
+ */
+@KtMongoDsl
+interface ConditionalOperators : ValueOperators {
+
+	/**
+	 * Decides between two [values][Value] depending on the evaluation of a boolean value.
+	 *
+	 * ### Example
+	 *
+	 * ```kotlin
+	 * class User(
+	 *     val name: String,
+	 *     val score: Int,
+	 *     val multiplier: Int,
+	 * )
+	 *
+	 * users.updateManyWithPipeline {
+	 *     set {
+	 *         User::score set cond(
+	 *             condition = of(User::multiplier) gt of(2),
+	 *             ifTrue = of(User::score) * of(User::multiplier),
+	 *             ifFalse = of(User::score)
+	 *         )
+	 *     }
+	 * }
+	 * ```
+	 *
+	 * ### External resources
+	 *
+	 * - [Official documentation](https://www.mongodb.com/docs/manual/reference/operator/aggregation/cond/)
+	 */
+	@OptIn(LowLevelApi::class)
+	@KtMongoDsl
+	fun <R : Any, T> cond(
+		condition: Value<R, Boolean>,
+		ifTrue: Value<R, T>,
+		ifFalse: Value<R, T>,
+	): Value<R, T> =
+		ConditionalValue(context, condition, ifTrue, ifFalse)
+
+	@OptIn(LowLevelApi::class)
+	private class ConditionalValue<Root: Any, Type>(
+		context: BsonContext,
+		private val condition: Value<Root, Boolean>,
+		private val ifTrue: Value<Root, Type>,
+		private val ifFalse: Value<Root, Type>,
+	) : Value<Root, Type>, AbstractValue<Root, Type>(context) {
+
+		@LowLevelApi
+		override fun write(writer: BsonValueWriter) = with(writer) {
+			writeDocument {
+				writeDocument("\$cond") {
+					write("if") {
+						condition.writeTo(this)
+					}
+
+					write("then") {
+						ifTrue.writeTo(this)
+					}
+
+					write("else") {
+						ifFalse.writeTo(this)
+					}
+				}
+			}
+		}
+	}
+}
diff --git a/dsl/src/commonMain/kotlin/aggregation/stages/Set.kt b/dsl/src/commonMain/kotlin/aggregation/stages/Set.kt
--- a/dsl/src/commonMain/kotlin/aggregation/stages/Set.kt
+++ b/dsl/src/commonMain/kotlin/aggregation/stages/Set.kt
@@ -76,6 +76,8 @@
 @KtMongoDsl
 interface SetOperators<T : Any> : CompoundExpression, ValueDsl, FieldDsl {
 
+	// region $set
+
 	/**
 	 * Replaces the value of a field with the specified [value].
 	 *
@@ -126,6 +128,259 @@
 		this.field.set(value)
 	}
 
+	// endregion
+	// region Conditional $set
+	// region setIf
+
+	/**
+	 * Replaces the value of a field with the specified [value], if [condition] is `true`.
+	 *
+	 * If [condition] is `false`, this operator does nothing.
+	 *
+	 * ### External resources
+	 *
+	 * - [`$set`](https://www.mongodb.com/docs/manual/reference/operator/update/set/)
+	 * - [`$cond`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/cond/)
+	 */
+	@Suppress("INVISIBLE_REFERENCE")
+	@KtMongoDsl
+	fun <@kotlin.internal.OnlyInputTypes V> Field<T, V>.setIf(condition: Value<T, Boolean>, value: Value<T, V>) =
+		this set cond(condition, value, of(this))
+
+	/**
+	 * Replaces the value of a field with the specified [value], if [condition] is `true`.
+	 *
+	 * If [condition] is `false`, this operator does nothing.
+	 *
+	 * ### External resources
+	 *
+	 * - [`$set`](https://www.mongodb.com/docs/manual/reference/operator/update/set/)
+	 * - [`$cond`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/cond/)
+	 */
+	@Suppress("INVISIBLE_REFERENCE")
+	@KtMongoDsl
+	fun <@kotlin.internal.OnlyInputTypes V> KProperty1<T, V>.setIf(condition: Value<T, Boolean>, value: Value<T, V>) =
+		this.field.setIf(condition, value)
+
+	/**
+	 * Replaces the value of a field with the specified [value], if [condition] is `true`.
+	 *
+	 * If [condition] is `false`, this operator does nothing.
+	 *
+	 * ### External resources
+	 *
+	 * - [`$set`](https://www.mongodb.com/docs/manual/reference/operator/update/set/)
+	 * - [`$cond`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/cond/)
+	 */
+	@Suppress("INVISIBLE_REFERENCE")
+	@KtMongoDsl
+	fun <@kotlin.internal.OnlyInputTypes V> Field<T, V>.setIf(condition: Value<T, Boolean>, value: V) =
+		this.setIf(condition, of(value))
+
+	/**
+	 * Replaces the value of a field with the specified [value], if [condition] is `true`.
+	 *
+	 * If [condition] is `false`, this operator does nothing.
+	 *
+	 * ### External resources
+	 *
+	 * - [`$set`](https://www.mongodb.com/docs/manual/reference/operator/update/set/)
+	 * - [`$cond`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/cond/)
+	 */
+	@Suppress("INVISIBLE_REFERENCE")
+	@KtMongoDsl
+	fun <@kotlin.internal.OnlyInputTypes V> KProperty1<T, V>.setIf(condition: Value<T, Boolean>, value: V) =
+		this.field.setIf(condition, value)
+
+	/**
+	 * Replaces the value of a field with the specified [value], if [condition] is `true`.
+	 *
+	 * If [condition] is `false`, this operator does nothing.
+	 *
+	 * ### External resources
+	 *
+	 * - [`$set`](https://www.mongodb.com/docs/manual/reference/operator/update/set/)
+	 * - [`$cond`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/cond/)
+	 */
+	@Suppress("INVISIBLE_REFERENCE")
+	@KtMongoDsl
+	fun <@kotlin.internal.OnlyInputTypes V> Field<T, V>.setIf(condition: Boolean, value: Value<T, V>) {
+		if (condition)
+			this.set(value)
+	}
+
+	/**
+	 * Replaces the value of a field with the specified [value], if [condition] is `true`.
+	 *
+	 * If [condition] is `false`, this operator does nothing.
+	 *
+	 * ### External resources
+	 *
+	 * - [`$set`](https://www.mongodb.com/docs/manual/reference/operator/update/set/)
+	 * - [`$cond`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/cond/)
+	 */
+	@Suppress("INVISIBLE_REFERENCE")
+	@KtMongoDsl
+	fun <@kotlin.internal.OnlyInputTypes V> KProperty1<T, V>.setIf(condition: Boolean, value: Value<T, V>) =
+		this.field.setIf(condition, value)
+
+	/**
+	 * Replaces the value of a field with the specified [value], if [condition] is `true`.
+	 *
+	 * If [condition] is `false`, this operator does nothing.
+	 *
+	 * ### External resources
+	 *
+	 * - [`$set`](https://www.mongodb.com/docs/manual/reference/operator/update/set/)
+	 * - [`$cond`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/cond/)
+	 */
+	@Suppress("INVISIBLE_REFERENCE")
+	@KtMongoDsl
+	fun <@kotlin.internal.OnlyInputTypes V> Field<T, V>.setIf(condition: Boolean, value: V) =
+		this.setIf(condition, of(value))
+
+	/**
+	 * Replaces the value of a field with the specified [value], if [condition] is `true`.
+	 *
+	 * If [condition] is `false`, this operator does nothing.
+	 *
+	 * ### External resources
+	 *
+	 * - [`$set`](https://www.mongodb.com/docs/manual/reference/operator/update/set/)
+	 * - [`$cond`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/cond/)
+	 */
+	@Suppress("INVISIBLE_REFERENCE")
+	@KtMongoDsl
+	fun <@kotlin.internal.OnlyInputTypes V> KProperty1<T, V>.setIf(condition: Boolean, value: V) =
+		this.field.setIf(condition, value)
+
+	// endregion
+	// region setUnless
+
+	/**
+	 * Replaces the value of a field with the specified [value], if [condition] is `false`.
+	 *
+	 * If [condition] is `true`, this operator does nothing.
+	 *
+	 * ### External resources
+	 *
+	 * - [`$set`](https://www.mongodb.com/docs/manual/reference/operator/update/set/)
+	 * - [`$cond`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/cond/)
+	 */
+	@Suppress("INVISIBLE_REFERENCE")
+	@KtMongoDsl
+	fun <@kotlin.internal.OnlyInputTypes V> Field<T, V>.setUnless(condition: Value<T, Boolean>, value: Value<T, V>) =
+		this set cond(condition, of(this), value)
+
+	/**
+	 * Replaces the value of a field with the specified [value], if [condition] is `false`.
+	 *
+	 * If [condition] is `true`, this operator does nothing.
+	 *
+	 * ### External resources
+	 *
+	 * - [`$set`](https://www.mongodb.com/docs/manual/reference/operator/update/set/)
+	 * - [`$cond`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/cond/)
+	 */
+	@Suppress("INVISIBLE_REFERENCE")
+	@KtMongoDsl
+	fun <@kotlin.internal.OnlyInputTypes V> KProperty1<T, V>.setUnless(condition: Value<T, Boolean>, value: Value<T, V>) =
+		this.field.setUnless(condition, value)
+
+	/**
+	 * Replaces the value of a field with the specified [value], if [condition] is `false`.
+	 *
+	 * If [condition] is `true`, this operator does nothing.
+	 *
+	 * ### External resources
+	 *
+	 * - [`$set`](https://www.mongodb.com/docs/manual/reference/operator/update/set/)
+	 * - [`$cond`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/cond/)
+	 */
+	@Suppress("INVISIBLE_REFERENCE")
+	@KtMongoDsl
+	fun <@kotlin.internal.OnlyInputTypes V> Field<T, V>.setUnless(condition: Value<T, Boolean>, value: V) =
+		this.setUnless(condition, of(value))
+
+	/**
+	 * Replaces the value of a field with the specified [value], if [condition] is `false`.
+	 *
+	 * If [condition] is `true`, this operator does nothing.
+	 *
+	 * ### External resources
+	 *
+	 * - [`$set`](https://www.mongodb.com/docs/manual/reference/operator/update/set/)
+	 * - [`$cond`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/cond/)
+	 */
+	@Suppress("INVISIBLE_REFERENCE")
+	@KtMongoDsl
+	fun <@kotlin.internal.OnlyInputTypes V> KProperty1<T, V>.setUnless(condition: Value<T, Boolean>, value: V) =
+		this.field.setUnless(condition, value)
+
+	/**
+	 * Replaces the value of a field with the specified [value], if [condition] is `false`.
+	 *
+	 * If [condition] is `true`, this operator does nothing.
+	 *
+	 * ### External resources
+	 *
+	 * - [`$set`](https://www.mongodb.com/docs/manual/reference/operator/update/set/)
+	 * - [`$cond`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/cond/)
+	 */
+	@Suppress("INVISIBLE_REFERENCE")
+	@KtMongoDsl
+	fun <@kotlin.internal.OnlyInputTypes V> Field<T, V>.setUnless(condition: Boolean, value: Value<T, V>) {
+		if (!condition)
+			this.set(value)
+	}
+
+	/**
+	 * Replaces the value of a field with the specified [value], if [condition] is `false`.
+	 *
+	 * If [condition] is `true`, this operator does nothing.
+	 *
+	 * ### External resources
+	 *
+	 * - [`$set`](https://www.mongodb.com/docs/manual/reference/operator/update/set/)
+	 * - [`$cond`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/cond/)
+	 */
+	@Suppress("INVISIBLE_REFERENCE")
+	@KtMongoDsl
+	fun <@kotlin.internal.OnlyInputTypes V> KProperty1<T, V>.setUnless(condition: Boolean, value: Value<T, V>) =
+		this.field.setUnless(condition, value)
+
+	/**
+	 * Replaces the value of a field with the specified [value], if [condition] is `false`.
+	 *
+	 * If [condition] is `true`, this operator does nothing.
+	 *
+	 * ### External resources
+	 *
+	 * - [`$set`](https://www.mongodb.com/docs/manual/reference/operator/update/set/)
+	 * - [`$cond`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/cond/)
+	 */
+	@Suppress("INVISIBLE_REFERENCE")
+	@KtMongoDsl
+	fun <@kotlin.internal.OnlyInputTypes V> Field<T, V>.setUnless(condition: Boolean, value: V) =
+		this.setUnless(condition, of(value))
+
+	/**
+	 * Replaces the value of a field with the specified [value], if [condition] is `false`.
+	 *
+	 * If [condition] is `true`, this operator does nothing.
+	 *
+	 * ### External resources
+	 *
+	 * - [`$set`](https://www.mongodb.com/docs/manual/reference/operator/update/set/)
+	 * - [`$cond`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/cond/)
+	 */
+	@Suppress("INVISIBLE_REFERENCE")
+	@KtMongoDsl
+	fun <@kotlin.internal.OnlyInputTypes V> KProperty1<T, V>.setUnless(condition: Boolean, value: V) =
+		this.field.setUnless(condition, value)
+
+	// endregion
+	// endregion
 }
 
 private class SetExpression<T : Any>(
diff --git a/dsl/src/commonTest/kotlin/aggregation/stages/SetTest.kt b/dsl/src/commonTest/kotlin/aggregation/stages/SetTest.kt
--- a/dsl/src/commonTest/kotlin/aggregation/stages/SetTest.kt
+++ b/dsl/src/commonTest/kotlin/aggregation/stages/SetTest.kt
@@ -16,10 +16,7 @@
 
 package opensavvy.ktmongo.dsl.aggregation.stages
 
-import opensavvy.ktmongo.dsl.aggregation.TestPipeline
-import opensavvy.ktmongo.dsl.aggregation.literal
-import opensavvy.ktmongo.dsl.aggregation.set
-import opensavvy.ktmongo.dsl.aggregation.shouldBeBson
+import opensavvy.ktmongo.dsl.aggregation.*
 import opensavvy.ktmongo.dsl.expr.filter.gt
 import opensavvy.prepared.runner.kotest.PreparedSpec
 import kotlin.text.Typography.dollar
@@ -57,6 +54,96 @@
 					}
 				]
 			""".trimIndent())
+	}
+
+	suite("setIf and setUnless") {
+
+		test("Aggregation values") {
+			TestPipeline<Target>()
+				.set {
+					Target::deathDate.setIf(of(Target::isAlive), of(12))
+				}
+				.shouldBeBson("""
+					[
+						{
+							"$set": {
+								"deathDate": {
+									"$cond": {
+										"if": "${dollar}isAlive",
+										"then": {
+											"$literal": 12
+										},
+										"else": "${dollar}deathDate"
+									}
+								}
+							}
+						}
+					]
+				""".trimIndent())
+		}
+
+		test("Kotlin values") {
+			TestPipeline<Target>()
+				.set {
+					Target::deathDate.setIf(of(Target::isAlive), 12)
+				}
+				.shouldBeBson("""
+					[
+						{
+							"$set": {
+								"deathDate": {
+									"$cond": {
+										"if": "${dollar}isAlive",
+										"then": {
+											"$literal": 12
+										},
+										"else": "${dollar}deathDate"
+									}
+								}
+							}
+						}
+					]
+				""".trimIndent())
+		}
+
+		test("Boolean condition") {
+			TestPipeline<Target>()
+				.set {
+					Target::deathDate.setIf(true, of(12))
+					Target::deathDate.setIf(false, of(13))
+				}
+				.shouldBeBson("""
+					[
+						{
+							"$set": {
+								"deathDate": {
+									"$literal": 12
+								}
+							}
+						}
+					]
+				""".trimIndent())
+		}
+
+		test("Boolean condition and Kotlin values") {
+			TestPipeline<Target>()
+				.set {
+					Target::deathDate.setIf(true, 12)
+					Target::deathDate.setIf(false, 13)
+				}
+				.shouldBeBson("""
+					[
+						{
+							"$set": {
+								"deathDate": {
+									"$literal": 12
+								}
+							}
+						}
+					]
+				""".trimIndent())
+		}
+
 	}
 
 })
diff --git a/dsl/src/commonTest/kotlin/expr/update/FieldUpdateTest.kt b/dsl/src/commonTest/kotlin/expr/update/FieldUpdateTest.kt
--- a/dsl/src/commonTest/kotlin/expr/update/FieldUpdateTest.kt
+++ b/dsl/src/commonTest/kotlin/expr/update/FieldUpdateTest.kt
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2024, OpenSavvy and contributors.
+ * Copyright (c) 2024-2025, OpenSavvy and contributors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -127,8 +127,8 @@
 
 		test("Multiple fields") {
 			update {
-				User::money inc 5.2
-				User::bestFriend / Friend::money inc -5.2f
+				User::money += 5.2
+				User::bestFriend / Friend::money += -5.2f
 			} shouldBeBson """
 				{
 					"$inc": {