Rules of Engagement (ROE) are driven by a mix of legal, military, and political factors. These dimensions can interact and overlap in subtle ways and must be carefully crafted to be easy to apply in combat situations without jeopardizing mission outcome and the warfighter's right to self-defense. Although trial and error may have sufficed in the past, the growing complexity of conflicts and the military and political ramifications of ineffective ROE (e.g., a friendly fire incident), make a simulation-based ROE evaluation system a high priority. This paper describes ROE3, a human behavior-modeling tool that supports tactics-independent representation of ROE. In our approach, ROE are defined as meta-knowledge that act as a constraint on the tactical choices selected by the synthetic entity. This is key to the flexibility of the system - tactics and ROE can be freely mixed and matched to investigate their interactions.