With the rise of the internet has come a rise in the importance of distributed systems. Distributed systems—groups of networked computers cooperating to run a single application or service—power modern web sites and communication services, infrastructure services like content-distribution networks and overlay networks, and parallel computations. With the complexity of distributed systems comes bugs: errors that affect a system’s correctness, performance, or both. Traditional debugging tools and methods do not apply well to distributed systems. Thus, new tools are needed that will enable programmers to find and fix bugs in distributed systems. These improvements will in turn improve the performance and reliability that end users experience. Many bugs reflect discrepancies between a system’s behavior and the programmer’s assumptions about that behavior. In this thesis, we show that expressing distributed system behavior as a set of causal paths and helping programmers separate