Hayy is an Islamic system, which emerged in the early 20th century. It is a system about the management of mosques and Islamic parishes.

Hayy is also called Masjid Hayy. It refers to a mosque that acts as the center of a vast Islamic region. Therefore sometimes people call it the big mosque or the center mosque while other mosques in the same region are called Masjid Sawma′ah, or small mosques.

According to this system, there is a relationship of governing and being governed between the two types of mosques. Generally a Masjid Hayy governs more than ten or even tens of Masjid Sawma′ah not only in terms of both religious affairs and personnel. That is to say, the Masjid Hayy appoints the head of a Masjid Sawma′ah.

It is also regulated that any important religious activities in the region, such as assemblies and festival prayers, should be held in the Masjid Hayy.

Besides, Masjid Hayy has the right to deal with all the civil litigations of Muslims in the region as well as to promulgate and interpret various Muslim religious laws.