Sunni Islam () is the largest branch of Islam. They are the branch of Islam that came through the Rashidun Empire, which started with Abu Bakr and ended by Ali ibn Abi Talib. Sunni beliefs are based on the Qu'ran and the Kutub al-Sittah. Sunnis make up around 90% of all Muslims. With approximately 1.8 billion followers, it is the largest religious denomination of any religion in the world. Catholicism is the second-largest. There are four sub-groups within Sunni Islam; Malikis, Hanafis, Hanbalis and Shafi'is.