Google’s guidelines on web sites.

A Googler’s guidelines on how to get back in if Google kicks you out for something naughty.

It is a little worrying though that the process seems a tad secretive. While Google does an excellent job of keeping the spammers out of their index, and I suppose they don’t want to give the spammers too much information on how it’s done, legitimate sites do get caught up in it from time to time (sometimes through ignorance), and there seems to be little in the way of feedback from Google about what a site might have done to get themselves banned.