Ayatollah, meaning sign of God, denotes a senior rank of achievement in Twelver Shia religious scholarship attained through advanced study at a hawza, a Shia seminary, typically requiring well over a decade of study progressing through increasingly advanced levels of jurisprudence, Quranic exegesis and Islamic philosophy, though, unlike a formal academic degree, the title carries no single centralized certifying body and is instead conferred informally through recognition by a scholar's own teachers and peers as his competence and reputation grow. An ayatollah stands below the still more senior rank of Grand Ayatollah and, in particular, below the smaller number of Grand Ayatollahs who achieve recognition as a marja-e taqlid, a source of emulation whose specific legal rulings a following of ordinary believers adopts, so that many ayatollahs teach, write and issue opinions of real scholarly weight within the seminary system without themselves becoming a marja with an independent following of lay adherents.
The major hawza cities, chiefly Qom in Iran and Najaf in Iraq, along with smaller centers such as Mashhad and Isfahan, each maintain their own networks of teachers and students through which an ayatollah's reputation and standing develop over a career that, for most, unfolds gradually across decades of teaching and scholarly output rather than through any single formal promotion or public announcement marking the transition from student to recognized ayatollah.