ISIS's Use of Sexual Violence in Iraq explores how and why the Islamic State organized and used sexual violence against Yezidi women in Iraq. Sexual violence in conflict is one the most devastating types of attack waged against non-combatants. It separates families, displaces communities, and perpetuates on-going social and psychological conflicts long after surviving victims are freed. It is a highly effective weapon that degrades and humiliates people when they are most vulnerable. Reports of executions, abductions, and sexual slavery among the Yezidi community at the hands of ISIS horrified the world, which witnessed some 5,000 women and girls reduced to sexual slavery. This qualitative case study tests three theories against the empirical evidence: evolution theory, feminist theory, and Strategic Rape Concept. Each theory will be tested in order to determine its explanatory strength, and to shed light on how ISIS's use of sexual violence can be explained. Due to the multilayered nature of the case study as it is current and highly complex, the research suggests that the elements pertaining to all three theories can collectively explain the role of sexual violence in ISIS's war for domination and control, and improve our understanding of how sexual violence is realized and perpetrated in the modern world.