Test planning for core-based system-on-a-chip (SOC) designs is necessary to reduce testing time and test cost. In this paper, we survey recent advances in test planning that address the problems of test access and constrained test scheduling for core-based SOCs. We describe several test access architectures proposed by research groups in industry and academia, as well as a wide range of methodologies for the optimization of such architectures. An extensive list of references to prior and current work in the SOC test planning domain is included.