This is a somewhat dated introduction from the time when 3.1 was still very new and lots of people were still using 3.0. (It's old enough that I consider a Pentium II class PC to be "fast" on one of the pages :-)

I haven't bothered to update it significantly since I believe most of the information here is still useful, even in the current version (3.6). Few if any of the truly backwards-incompatible features (like the infamous 3.0 "halo") appear in this overview. I believe that if the scenes I describe don't render immediately in 3.5 or 3.6, fairly minimal and obvious revision or setting the #version directive to 3.0 will suffice.