The analysis found no difference in the self-reported arrest decisions of officers in relation to agency size. The study used officers from two small police departments, one intermediate size, and one large police department. There was no indication that officer compliance with mandatory arrest policies deteriorated as the size of a department increased, under the theory that large agencies are more “loosely coupled,” which leads to less monitoring and attention to officers’ use of discretion. Situational variables were apparently the controlling influence on an officer’s arrest decision under a mandatory arrest law for domestic violence incidents. Officers’ decisions in relation to the situational factors in the vignettes indicate that when a domestic-violence victim suffers a minor or serious injury, officers interpret such incidents as satisfying the threshold needed for mandatory arrest. The presence of an order of protection was certain to produce an arrest decision under a State law requiring an arrest if the order was violated. Apparently, officers govern their decisions to make an arrest in a domestic violence incident by the provisions of mandatory arrest legislation regardless of the size of their agency and the associated tightness or looseness of officer monitoring/supervision. The survey instrument used a factorial design to measure the impact of situational variables on officer decisionmaking. Vignettes randomly varied the level of each circumstance of an incident among vignettes. Officers were asked to indicate the likelihood of making an arrest, on a scale of one to five. 3 tables, 51 references, and descriptions of circumstances that varied in their inclusion in vignettes