Xenopus laevis frog tadpoles near the time of hatching have proved to be an excellent model system in which to explore the neural mechanisms responsible for the initiation, maintenance, sensory adaptation, and termination of rhythmic locomotor activity in vertebrates. The underlying neural network is one of the most completely understood in any vertebrate. Detailed knowledge has accrued over the last 40 years, highlighting conserved operational features of vertebrate rhythm generators and serving as an invaluable platform from which to investigate associated issues of fundamental importance in neuroscience, such as motor program switching, transmitter corelease, network development, neuromodulation, and metamodulation of network operation. There are many advantages of this simple model system, including the presence of a well-defined network output that relates directly to the behavior of the animal under study (namely, swimming locomotion).