Some interesting info...
(From
http://www.religioustolerance.org/worldrel.htm)
(The numbers represent how many people supposedly belong to that religion).
Christianity 2,015 million (dropping)
Islam 1,215 million (growing)
No religion 925 million (dropping)
Hinduism 786 million (stable)
Buddhism 362 million (stable)
Atheists 211 million
Chinese folk rel - 188 million
New Asian rel. - 106 million
Tribal Religions Prehistory - 91 million
Other Various - 19 million
Sikhism - 16 million
Judaism - 18 million
Shamanists Prehistory - 12 million
Spiritism - 7 million
Confucianism - 5 million
Baha'i Faith - 4 million
Jainism - 3 million
Shinto - 3 million
Zoroastrianism - 0.2 million
I think it is important to note things like, for example, how many people label themselves Christian, and how many actually have a firm belief of Christianity.
For example, there are all those people that are like, "Yeah, I suppose I am Christian". The ones that say, "I was brought up with it, I dont know anything about it, but I dont care, so I will just say I am christian".
If you take people like this into account, and I have talked with many dedicated Christians about this who agree with me, that you would then actually only have perhaps a few hundred million Christians, instead of the supposed 2 billion.
I am not sure about the validity of these statistics, as I am quite sure there would be more than 211 million Atheists in the world; and I was quite certain there were more Budhists than mentioned above.
However, I suppose it is a good basic outline.