The spring-loaded inverted pendulum (SLIP) describes gait with a point mass rebounding on spring legs. The model captures the center of mass dynamics observed in running animals and has become a basic gait template in biomechanics and robotics for studying the dynamics and control of compliant legged locomotion. This chapter provides an overview of gait based on the SLIP model. The standard SLIP model for describing sagittal plane locomotion is introduced through a review of early model developments in the biomechanics and robotics communities. Related legged platforms are presented. Methods are then discussed for studying the dynamics and control of locomotion with this model, including approximate solutions to the stance dynamics, return map analysis of periodic gait, and optimal control approaches for getting stable and robust running behavior. Finally, generalizations of the SLIP model and its analysis methods are highlighted for performing multistep planning, expanding to locomotion in 3-D environments, generating walking and gait transitions, and embedding in humanoids and other legged robots. The chapter closes with suggestions for future directions that will likely help to grow the utility of the SLIP model as a gait template for agile, stable, and robust locomotion on compliant legs.