An exception handling system for a packet processing system is described. In this exception handling system, there are several exception handlers. One of the exception handlers is selected based on packet processing state data relating to a packet undergoing processing by the packet processing system. The selected exception handler is configured to check for the presence of one or more potential exception conditions associated with the selected exception handler. If one or more of these potential exception conditions are determined to be present, a packet processor selectively modifies the packet processing state data relating to the packet.