diff --git a/spec/draft/API_specification/set_functions.rst b/spec/draft/API_specification/set_functions.rst
index addf31e1f..cf2af9f68 100644
--- a/spec/draft/API_specification/set_functions.rst
+++ b/spec/draft/API_specification/set_functions.rst
@@ -18,6 +18,7 @@ Objects in API
:toctree: generated
:template: method.rst
+ isin
unique_all
unique_counts
unique_inverse
diff --git a/src/array_api_stubs/_draft/set_functions.py b/src/array_api_stubs/_draft/set_functions.py
index 7fee77ecb..5afeb2836 100644
--- a/src/array_api_stubs/_draft/set_functions.py
+++ b/src/array_api_stubs/_draft/set_functions.py
@@ -1,7 +1,50 @@
-__all__ = ["unique_all", "unique_counts", "unique_inverse", "unique_values"]
+__all__ = ["isin", "unique_all", "unique_counts", "unique_inverse", "unique_values"]
-from ._types import Tuple, array
+from ._types import Tuple, Union, array
+
+
+def isin(
+ x1: Union[array, int, float, complex, bool],
+ x2: Union[array, int, float, complex, bool],
+ /,
+ *,
+ invert: bool = False,
+) -> array:
+ """
+ Tests whether each element in ``x1`` is in ``x2``.
+
+ Parameters
+ ----------
+ x1: Union[array, int, float, complex, bool]
+ first input array. **May** have any data type.
+ x2: Union[array, int, float, complex, bool]
+ second input array. **May** have any data type.
+ invert: bool
+ boolean indicating whether to invert the test criterion. If ``True``, the function **must** test whether each element in ``x1`` is *not* in ``x2``. If ``False``, the function **must** test whether each element in ``x1`` is in ``x2``. Default: ``False``.
+
+ Returns
+ -------
+ out: array
+ an array containing element-wise test results. The returned array **must** have the same shape as ``x1`` and **must** have a boolean data type.
+
+ Notes
+ -----
+
+ - At least one of ``x1`` or ``x2`` **must** be an array.
+
+ - If an element in ``x1`` is in ``x2``, the corresponding element in the output array **must** be ``True``; otherwise, the corresponding element in the output array **must** be ``False``.
+
+ - Testing whether an element in ``x1`` corresponds to an element in ``x2`` **must** be determined based on value equality (see :func:`~array_api.equal`). For input arrays having floating-point data types, value-based equality implies the following behavior. When ``invert`` is ``False``,
+
+ - As ``nan`` values compare as ``False``, if an element in ``x1`` is ``nan``, the corresponding element in the returned array **must** be ``False``.
+ - As complex floating-point values having at least one ``nan`` component compare as ``False``, if an element in ``x1`` is a complex floating-point value having one or more ``nan`` components, the corresponding element in the returned array **must** be ``False``.
+ - As ``-0`` and ``+0`` compare as ``True``, if an element in ``x1`` is ``±0`` and ``x2`` contains at least one element which is ``±0``, the corresponding element in the returned array **must** be ``True``.
+
+ When ``invert`` is ``True``, the returned array **must** contain the same results as if the operation is implemented as ``logical_not(isin(x1, x2))``.
+
+ - Comparison of arrays without a corresponding promotable data type (see :ref:`type-promotion`) is unspecified and thus implementation-defined.
+ """
def unique_all(x: array, /) -> Tuple[array, array, array, array]:
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