  In classical contract theory, we usually impose two assumptions: delegated
contracts and perfect commitment. While the second assumption is demanding, the
first one suffers no loss of generality. Following this tradition, current
common-agency models impose delegated contracts and perfect commitment. We
first show that non-delegated contracts expand the set of equilibrium outcomes
under common agency. Furthermore, the powerful menu theorem for common agency
(Peters (2001) and Martimort and Stole (2002)}) fails for either non-delegated
contracts or imperfect commitment. We identify canonical contracts in such
environments, and re-establish generalized menu theorems. Given imperfect
commitment, our results for common-agency models are analogous to those in
Bester and Strausz (2001) and Doval and Skreta (2012) for the classical
contract theory, which re-establish the revelation principle.
