This article presents and explains the physics learning system called Investigative Science Learning Environment (ISLE), which features carefully selected observational videos as a focus of instruction. In ISLE, all experiments that students encounter can be placed into one of three categories according to their roles: observational (experiments that are used to generate explanations), testing (used to test explanations), or application (experimental problems to solve for which one needs to synthesize multiple explanations and/or relations). The video Web site follows this scheme, helping an instructor form a learning progression that mirrors the process of doing physics.