Shiite religious leaders can hold a number of different titles, but those at the top of the hierarchy have undertaken exhaustive study, teaching and writing in seminaries housed in a handful of holy Shiite cities in the Middle East.
The premier place is the Iraqi city of Najaf, where the holiest Shiite shrine is located and where Grand Ayatollah Ali al Sistani studied.
Mullahs are the most basic level of Shiite cleric. They may still be continuing their religious training or have stopped after a few years and hold such positions as prayer leader or administrator of a shrine.
Only a fraction of mullahs complete the average 15 years of study needed to rise to the next rank, "mujtahed," or scholar. These are the clerics who wield religious authority, based on their expertise in Islamic verse, law and science. A mujtahed must also have the backing of other acknowledged mujtaheds, as well as tacit acceptance by lay Shiites.
Mujtaheds start out with the title of "hojjatoleslam" and, depending on their skills and support from fellow mujtaheds, may one day be referred to as an ayatollah. The most intellectual, talented and respected among those are called grand ayatollahs.
Seasoned ayatollahs and grand ayatollahs become "marjahs" or spiritual leaders, once they've published their interpretations of Islamic law, developed a following among lay Shiites and lower-ranking clergy and received financial contributions from their followers.
Lay Shiites and mullahs are expected to obey a marjah's "fatwas" or religious decrees, although they choose which marjah to follow. It is common for several prominent and occasionally competing marjahs to rule at the same time.
(c) 2003, Knight Ridder/Tribune Information Services.