In recent years, as our understanding of the pattern-generating networks responsible for a variety of behaviors has increased, the interactions of multiple neural networks have been examined in a number of systems. These studies have shown that functionally related pattern generators can interact extensively, and that the extent to which two or more of these networks interact is not fixed, but can be altered by neuromodulators. Furthermore, a number of studies have begun to elucidate the mechanisms responsible for those interactions. In the crustacean stomatogastric system, for example, neurons can switch between different pattern generators, and whole networks can fuse into single patterns. In addition, several networks can be dismantled, and their components used to generate a new network. The mechanisms responsible for these changes are the same as those involved in other circuit re-configurations, namely alterations of both intrinsic membrane properties of component neurons and alterations in the strength of synapses within the networks.