We study the role of a relatively new type of external firm monitor, an on-site government-appointed Corporate Monitor, and assess whether such appointments reduce firms' propensity to violate laws. Using a sample of deferred and nonprosecution agreements, we first document the determinants of Monitor appointment. We find firms that voluntarily disclose wrongdoing and have more independent directors are less likely to have Corporate Monitors, whereas those with more severe infractions, mandated board changes, and increased cooperation requirements are more likely to have Monitors. We find such appointments are associated with an 18%–25% reduction in violations while the Monitor is on site, however, the effect does not persist after the Monitorship ends. Using a semisupervised machine learning method to measure changes in firms' ethics and compliance norms, we find that the reduction in violations is associated with changes in ethics and compliance that also do not persist. Finally, we document that firms under Monitorship experience a persistent reduction in innovation, highlighting a previously unexplored cost of these interventions. Overall, our results suggest that, although Corporate Monitors on site are associated with fewer violations, firms revert to previous levels of violations following Monitors' departure.