States often violate international agreements, both accidentally and intentionally. To process complaints efficiently, states can create formal, pretrial procedures in which governments can negotiate with litigants before a case ever goes to court. If disputes are resolved during pretrial negotiations, it can be very difficult to tell what has happened. Are governments coming into compliance? If so, are they only doing so when they have accidentally committed a violation or even when they are intentionally resisting? Or are challenges simply being dropped? This paper presents a formal model to address these questions. We develop our theory in the context of the European Union (EU). To test our model, we collect a new dataset of over 13,000 Commission infringement cases against EU member states (2003–2013). Our results suggest that accidental and intentional noncompliance both occur, but that intentional noncompliance is more common in the EU. We find that the Commission is an effective, if imperfect, monitor and enforcer of international law. The Commission can correct intentional noncompliance, but not always. It strategically drops cases that it believes it is unlikely to win.