There are two million different species in the world - plants, bacteria, animals, everything.
And what scientists call them has happened haphazardly - so for example if you say Anthrax, you could be talking about the bacterium, or you could be talking about a kind of fly. Confused?
Well an international project called the Open Tree of Life is sorting it out - they already have a list of 1.9 million species without that kind of ambiguity and should have the complete list next year.
And scientists at Imperial College have made a really cool computer "map" of the tree of life. You navigate round it just like Google maps. Zoom in to an individual species, and it will tell you how old it is and whether it's threatened or even extinct.
You get a real idea of how species are related - and it's just great fun.