There are a total of 21 Merit Badges required for the rank of Eagle.

12 of these badges are Eagle Required "White Bands"  (merit badges with white/silver border stitching around the edges).

The remaining 9 (or more if you choose) may be any badges from among the remaining 109 non-Eagle required "Green Band" merit badges (badges with green stitching around the border).

While there are 17 possible Eagle Merit Badges, there are some that are "optional".  Refer to the picture to clearly understand which badges qualify for Eagle, and which ones do not.   Earning MORE THAN ONE of the optional badges will NOT afford you the choice to NOT earn other required badges, but "extra" Eagle badges can be counted towards the mandatory total of 21.