We propose and quantify a future role for photonic crystals in optical signal processing. We analyze the optical signal processing functionality of nonlinear periodic structures. By elaborating an analytical model and employing numerical simulations, we explore the performance of proposed devices. We prove that the proposed limiters provide true limiting by clamping the transmitted intensity at a level which is independent of the incident intensity. We explore the response of optical switches for signal and pump beams having the same and different frequencies. We describe and quantify the performance of the proposed structures in the realization of optical hard-limiters. We explore the performance of an all-optical logic gate whose forward- directed output implements a binary AND and whose backward- directed output implements an OR function. In addition we prove that the for fabrication errors as large as 10%, qualitative device functionality remains, with performance only modestly degraded.