I have been quite puzzled for some time with the concept of Diffeomorphic Invariance. Here is what I think about it, 1) Diffeomorphic Invariance is the invariance of the theory under general coordinate transformations. For instance the Einstein-Hilbert action is diffeomorphic invariant. 2) Poincare Invariance : The invariance of the equations of physics under rotations and translations. Should Poincare be thought of as an Active Diffeomorphism? And if it really can be, would it mean that poincare invariance is always implied when a system has diffeomorphsim invariance? Thanks!