An account of the concept from a Shia perspective.

An academic paper (by Knut S Vikør, University of Bergen) analyses the use of the concept by reforming thinkers in the 19th century.

An article from Wikipedia.

Report of a conference in 2004 sponsored by the United States Institute of Peace and the Center for the Study of Islam and Democracy entitled "Ijtihad: Reinterpreting Islamic Principles for the Twenty-first Century."