Abstract: An increasing number of developers face the difficult task of debugging distributed asynchronous programs. This trend has outpaced the development of adequate debugging tools and currently, the best option for many is an ad hoc patchwork of sequential tools and printf debugging. This paper presents Causeway, a postmortem distributed debugger that demonstrates a novel approach to understanding the behavior of a distributed program. Our message-oriented approach borrows an effective strategy from sequential debugging: To find the source of unintended side- effects, start with the chain of expressed intentions. We show how Causeway's integrated views - describing both distributed and sequential computation - help users navigate causal pathways as they pursue suspicions. We highlight Causeway's innovative features which include adaptive, customizable event abstraction mechanisms and graphical views that follow message flow across process and machine boundaries.