His death was announced by his movement, Adl wal Ihsan (Justice and Spirituality).
During the Arab Spring, Mr. Yassine’s group was an important part of the pro-democracy movement that demonstrated in the streets for much of 2011 for political reform and an end to corruption.
The bearded and veiled members of his group marched side by side with left-wing and secular activists, calling for less power for the hereditary monarchy and more power for elected officials.
Since the election victory of a moderate Islamist opposition party last month, Mr. Yassine’s movement has largely remained quiet, apparently giving the new government time to enact reforms.
Formed in 1987, Adl wal Ihsan is officially banned but tolerated, though its members are frequently harassed or arrested by the police, and Mr. Yassine spent nine years under house arrest. The movement advocates an Islamic state and an end to the monarchy. Its following is believed to be in the hundreds of thousands.
Born in Marrakesh in 1928, Mr. Yassine worked for the Education Ministry and wrote two books advocating an Islamic state in Morocco before he rose to fame in 1974 by publishing “Islam or the Deluge,” an open letter to King Hassan II. Mr. Yassine accused the king of corruption and subservience to Western mores, questioned whether he was a true Muslim and called on him to step down.
Mr. Yassine was well acquainted with the classics of Western culture, but he did not want to see Morocco slide toward Westernization. He wrote that “our democracy” is not a Western democracy that “begins at pagan Athens and ends in advanced modern societies as a secularist practice, atheistic and immoral.”
After King Hassan died in 1999 and his son assumed the throne as Mohammed VI, Mr. Yassine challenged the new king in a 35-page memorandum, made public the next year, blaming the monarchy for Morocco’s social, economic, and political difficulties.
Nonetheless, King Mohammed released Mr. Yassine from house arrest in May 2000 in a string of gestures intended to show a break with the past.

Abdesslam Yassine (1928 – December 13, 2012) was the leader of the Moroccan Islamist organisation Al Adl Wa Al Ihssane (Justice and Charity).[1]
Yassine was born in Marrakesh. He worked as a teacher and a school inspector for the Ministry of Education, and from 1965 on, was a member of one of the most famous Moroccan Sufi brotherhoods, the Boutchichiyya.[2] Yassine reportedly fell out with the leadership of the brotherhood over its refusal to engage more directly in political matters, and founded his own organisation. Yassine was jailed in a mental asylum for three years for publishing an open letter to King Hassan II denouncing his rule as unIslamic. Following his release he was kept under house arrest for many years, before eventually being released in the early years of the rule of King Mohammed VI.[3] Yassine's many publications include L'Islam ou le Deluge (Islam or the Flood),[4] probably the best known of his works. He died, aged 84, on 13 December 2012.[1]