This report summarized runtime system challenges for exascale computing, that follow from the fundamental challenges for exascale systems. Some of the key exascale challenges that pertain to runtime systems include parallelism, energy efficiency, memory hierarchies, data movement, heterogeneous processors and memories, resilience, performance variability, dynamic resource allocation, performance portability, and interoperability with legacy code. In addition to summarizing these challenges, the report also outlined different approaches to addressing these significant challenges that have been pursued by research projects in the DOE-sponsored X-Stack and OS/R programs. It also included a chapter on deployment opportunities for vendors and government labs to build on the research results from these projects.