The Encyclopaedia of Islam (EI) is a reference work that facilitates the academic study of Islam. It is published by Brill and provides information on various aspects of Islam and the Islamic world. It is considered to be the standard reference work in the field of Islamic studies. The first edition was published in 1913–1938, the second in 1954–2005, and the third was begun in 2007.

Brill Academic Publishers, also known as E. J. Brill, Koninklijke Brill, Brill, is a Dutch international academic publisher of books and journals.