Software process models are sophisticated and large specifications aimed at organizing and managing software development. Their formal specification demands an enormous effort, but once specified there are few approaches and even fewer tools that aid the process engineer to analyze the quality of the process. For the last five years we have aided software companies in specifying their software processes and we have found a series of error patterns that indicate the potential presence of misconceptions or misspecifications. This paper presents these patterns, characterizes the kinds of errors they potentially reveal, and details how errors could be localized within a software process model. To assist process engineers to analyze the quality of their processes, we provide Avispa, a tool that graphically renders different aspects of a process model and highlights potential errors as intuitive and comprehensible indicators. The approach and the supporting tool are illustrated by ap...