An iwan (Persian: ایوان eyvān, Arabic: إيوان ’īwān, also spelled ivan) is a rectangular hall or space, usually vaulted, walled on three sides, with one end entirely open. The formal gateway to the iwan is called pishtaq, a Persian term for a portal projecting from the facade of a building, usually decorated with calligraphy bands, glazed tilework, and geometric designs. Since the definition allows for some interpretation, the overall forms and characteristics can vary greatly in terms of scale, material, or decoration.

Iwans are most commonly associated with Islamic architecture; however, the form is pre-Islamic Iranian in origin and was invented much earlier and fully developed in Mesopotamia around the third century CE, during the Parthian period.