Ayatollah Sayyid Ali Hussaini Sistani is a Shiite authority and a teacher of advanced courses of fiqh and usul al-fiqh in Najaf. He studied in the Islamic seminary of Mashhad, Qom and Najaf. He attended the lectures of Ayatollah Burujirdi, Sayyid Muhammad Hujjat Kuhkamara'i, and Ayatollah al-Khoei.
In 1960-1 when he was 31 years old, al-Sayyid 'Ali al-Sistani received permissions for ijtihad from two of his teachers, Ayatollah al-Khoei and Shaykh Husayn al-Hilli. After Ayatollah al-Khoei's demise on August 8, 1992, Ayatollah al-Sistani took over the marja'iyya (Shiite authority). After the deaths of Sayyid 'Abd al-A'la Sabziwari and Sayyid Muhammad Rida Gulpayigani in 1414/1993 as well as Muhammad 'Ali Araki and Sayyid Muhammad Ruhani, his marja'iyya became more wide-ranging.