Which is the most widely spread religion in this world and why?

Christianity is the most widespread and largest religion; over 30 % of the world's population, Islam about 20%. In terms of number of countries in which the religion has a significant presence, Christianity is also the most widespread followed by the Baha'i faith. The fastest growing depends how you measure it, Islamic claims that Islam is the fastest growing religion should be approached with degree of scepticism. Sometimes these are based on the high birthrate in Muslim countries or immigration into other countries. If you are talking about converts between 1990 and 2000 there were under a million new converts to Islam but in the same period there were nearly 3 million converts to Christianity. Other sources make this differance greater still. all the best urban

According to a census taken in 2005, Christianity (both catholic and protestant) represents 33% of the world population while Islam is at 21%. Next in line is the non-religious at 16% and then Hinduism at 14%. I think right now, though, Islam is the fastest growing religion.

I think Islam is the most widely spread religion in the world. I think that is base on survery.