A new 12th edition of the Boy Scout Handbook (34622) was issued in the summer of 2009. That book contains new requirements for each rank, which did not officially take effect until January 1, 2010.

If a Scout has started work toward a rank before January 1, 2010, using requirements that were current before January 1, 2010, he may complete that rank only using the old requirements. Any progress toward a rank that is begun after January 1, 2010, must use the requirements as they are presented in the Boy Scout Handbook (34622) or in Boy Scout Requirements book (33216).

Scouts starting work on any of these badges after January 1, 2010, must use the new requirements.

Note that if a scout has any of the rank requirements 'signed off' with a date prior to 2010, he is considered to have started work on this rank and may use the old requirements.

A PDF file which summarizes the changes may be found here.