Intimate partner homicide (IPH) accounts for one-fifth of U.S. homicides, with the majority of IPH and nearly all (91.6%) of intimate-partner related homicide-suicides (IPH-S) committed by firearms. While much is known about the frequency by which IPH is committed by firearms, research is far more limited regarding how victim/perpetrator firearm access, ownership, and behaviors affect IPH and IPH-S risk. We propose a case-control study in two states (Maryland and Texas) chosen to provide robust interstate firearm comparisons, as well as demographic, geographic and relevant law diversity. We will collect case file (medical examiner, police, prosecutor) and interview data to compare the histories of IPH victims (cases) to those of a random sample of individuals who experienced non-fatal physical IPV in the past two years (controls). The study will accomplish the following: (1) Obtain a count of firearm-related IPH and IPH-S across multiple subgroups through triangulation of data from multiple sources; (2) Describe the context of IPH and IPH-S, including precipitating events, relationship history, and perpetrator characteristics such as prior suicidality and prior substance abuse; (3) Assess the strength of firearm access, ownership, and/or use as risk factors for IPH and IPH-S, attending to intersections with risk factors at the family (e.g., abuse history), community (e.g., community violence), social and environmental levels (e.g., state firearm policies, accessibility of social services); (4) Identify differential patterns of risk between firearm-related and non-firearm related IPH, and between firearm-related IPH and IPH-S; (5) Examine patterns of gun ownership behaviors and attitudes in relation to IPH and IPH-S. We will create a database that will combine data across current data collection endeavors, creating a foundation for future funding. Findings will inform future evidence-based, multiple-level prevention interventions and allow policy makers and practitioners to develop and refine risk-informed approaches to reduce and prevent lethal IPV outcomes.