It is our great pleasure to welcome you to the 9th Workshop on Parallel and Distributed Systems: Testing, Analysis, and Debugging - PADTAD'11. PADTAD is a workshop that brings together researchers from academia and practitioners from industry to promote the development of techniques and tools that aid in testing, analysis, and debugging of multi-threaded, parallel and distributed software. The quest to exploit concurrency at all levels—from hardware through applications—has made it imperative that researchers develop robust methods for testing, analyzing, and debugging concurrent systems. Of the many forums that cater to the need of researchers to assemble and discuss common issues they face and solutions they seek to refine, PADTAD is unique in that it intersperses technical papers with in depth discussion. This year, we are fortunate to receive generous support from Intel and IBM Research, which greatly facilitates the organization of PADTAD 2011.