In the United States, all 50 states and the District of Columbia have enacted statutes that allow police officers to make warrantless arrests for domestic violence given probable cause; however, state laws differ from one another in multiple, important ways. Research on domestic violence warrantless arrest laws rarely describe them as anything more than discretionary, preferred, or mandatory, either within their analyses or within the texts of their publications; researchers, and their audiences, may not be aware of the vast and potentially important differences among these laws. In this article, we list the domestic violence warrantless arrest laws for each state, and discuss them in terms of five common elements: the phrasing of the arrest authority; whether additional factors to domestic violence are required to trigger the arrest authority; qualifications to the arrest authority; time limits for warrantless arrest to occur; and whether police officers are required to report why they made a dual or no arrest. We then analyze the common elements of the laws, paying particular attention to how they may encourage or discourage the arrest of alleged domestic violence perpetrators. It is critical that researchers, advocates, and policymakers are aware of these variations in state statutes when conducting or interpreting research or making policy recommendations. (Contains 2 tables.)