After the major evolutionary shift from aquatic to terrestrial environments, many vertebrates retained the ability to swim, and some even became secondarily aquatic. The differing constraints of terrestrial and aquatic environments have shaped the evolution of specific morphologies and kinematics. Aquatic locomotion either uses undulations of the body and tail, paddling of the limbs or both simultaneously. Despite many studies on swimming in fishes, little research exists on swimming in tetrapods with sprawling postures, such as lizards. Most lizards have retained the ability to swim, and some are semi-aquatic. Here we present a comparative study of 28 lizard species and one snake, in which we quantified swimming performance and kinematics as well as the impact of morphology. We found that velocity, tail wave velocity, and thrust efficiency were marginally impacted by habitat use and that thrust efficiency was impacted by clade. Lateral compression of the tail decreased velocity and Froude number, and relatively long tail decreased velocity. We also found that a greater frontal head area was associated with a greater tail wave velocity but lower thrust efficiency. This suggests that morphological adaptations are important for propulsive efficacy and for facilitating drag reduction. Velocity was primarily modulated by increasing undulatory wavelength and frequency, while amplitude had little effect. Increased Froude number was associated with increased wavelength and frequency but not amplitude, and thrust efficiency was only significantly affected by wavelength. When lizards paddled with their limbs, amplitude and frequency increased, but performance did not. Thus, it is evident that undulatory kinematics vary with appendicular kinematics. Amplitude of undulations along the body decreased from the head to the pectoral girdle and then increased to the tail for all lizards, while amplitude simply increased posteriorly from the head in the snake. This suggests that amplitude along the body may be constrained in lizards either by morphological or hydrodynamic limitations.