A mosque (/mɒsk/; Arabic:مسجد masjid pl. مساجد masājid), sometimes spelt mosk, is a place of worship for followers of Islam.

There are strict and detailed requirements in Sunni fiqh for a place of worship to be considered a masjid, with places that do not meet these requirements regarded as musallas. There are stringent restrictions on the uses of the area formally demarcated as the masjid (which is often a small portion of the larger complex), and, in the Sharia, after an area is formally designated as a masjid, it remains so until the Last Day.

Quba Mosque is the first mosque in history, and mosques have developed significantly since Quba mosque. Many mosques have elaborate domes, minarets, and prayer halls. Mosques originated on the Arabian Peninsula, but are now found in all inhabited continents. The mosque serves as a place where Muslims can come together for salah (prayer) (Arabic: صلاة‎, ṣalāt) as well as a center for information, education, and dispute settlement. The imam leads the prayer.