The Scrum Guide by Ken Schwaber and Jeff Sutherland is an evolving document.  We will try to keep here the latest version.

Scrum GuideFeb2010.pdf

This is a newer edition, from July 2011:

Scrum Guide - 2011-1.pdf

Bear in mind that this guide is talking about the bare framework of Scrum. It does not attempt to talk about Release Planning, for example, which almost everyone must do.  There are many other things a Scrum Team must do. Not all of these can be articulated in this short guide. Nor can everything be fully explained in a much longer book.  So, like Scrum, this Scrum Guide expects you to think for yourself taking into account your specific situation.