History of Religions...

The four largest religious groups by population, estimated to account for between 5 and 6 billion people, are Christianity, Islam, Buddhism and Hinduism.

Four largest religion	Adherents	% of world population	Article
World population	6.8 billion	Figures taken from individual articles:
Christianity	1.9 billion – 2.1 billion	29% – 32%	Christianity by country
Islam	1.3 billion – 1.57 billion	19% – 21%	Islam by country
Buddhism	500 million – 1.5 billion	7% – 21%	Buddhism by country
Hinduism	950 million – 1 billion	14% – 20%	Hinduism by country
Total	4.65 billion – 6.17 billion	68.38% – 90.73%