At what age can you spay a puppy?

The risk is lowest when the puppy is spayed before she is six months old, but this can be done before she is two years old. It is also effective to spay a dog before she is eight years old.

Edit: Above was spot-on traditional. Especially for working dogs, it has been replaced by spay (or neuter) them later rather than early. For females, after the first heat or litter; males at about a year and a half (before 9 months and your going to get an underdeveloped dog). Early erodes development hormones requisite for achieving their potential.