We propose a novel segment-based light transport framework that uses segments as the basic unit of light transport. Unlike vertex-based formulations, our segment-based formulation naturally accommodates the disconnected subpaths encountered in photon density estimation and path filtering methods, and opens the door to a wide range of new rendering methods that consider segments as a sampling primitive. To facilitate the development of segment-based rendering methods, we introduce several segment sampling techniques and estimation strategies, including a highly-performant recursive estimator. One of our key contributions is a general-purpose segment sampling framework based on marginal multiple importance sampling (MMIS). To demonstrate the practicality of our sampling framework, we show how it allows us to easily implement a robust bidirectional path filtering method — challenging under a vertex-based formulation — achieving superior filtering efficiency and convergence compared to state-of-the-art approaches.