It is our great pleasure to welcome you to the 16th ACM Symposium on Principles and Practice of Parallel Programming -- PPoPP'11. PPoPP continues to be the premiere forum where researchers present their work on all aspects of parallelism and concurrency: algorithms and applications, programming models, languages, and environments, system software and runtime systems, and theoretical foundational work. As our industry continues to move toward parallel systems, from large-scale supercomputers to multicore mobile devices, such as smart phones and tablets, research work on concurrency is needed to support developers at all levels of the execution stack.