Ken Schwaber and Jeff Sutherland, the co-founders of Scrum, have been working together and with the Scrum community on updating the official Scrum Body of Knowledge, the Scrum Guide. Today, they have released this update through Scrum.org, the home of Scrum, and your source for Scrum training, assessment, and certification.
The core principles of Scrum remain, but misunderstandings have been clarified and techniques have been removed. The "Definitive Guide to Scrum," focuses on the framework, rules, and ceremonies of Scrum. Emphasis is placed on the roles of the Scrum Team and understanding of their responsibilities, as opposed to the strategies and techniques involved in fulfilling those roles and responsibilities.
Along with the release of the the Scrum Guide 2011, Ken and Jeff are making available a statement of these refinements. This message from Ken and Jeff can also be found on Scrum.org/scrumguides. Currently, The Scrum Guide 2011 can be found in English on Scrum.org, with more translations expected as translation teams complete them.