Interaction with the Interstellar Medium (ISM) cannot be ignored in models of PN evolution and shaping. As first pointed out by Villaver et al. (2003 ApJ 585 L49), this interaction begins during the AGB phase. We have run extensive sets of 3D simulations, from the beginning of the AGB superwind until the end of the PN phase to study this interaction. We find ISM interaction strongly affects the outer structures. The simulations predict parsec-size shells to be common. The structure and brightness of ancient PNe is largely determined by the ISM interaction during the AGB and the majority of PNe will have tail structures.