While most civil wars today are fought within Muslim-majority states and, frequently, by armed groups that self-identify as Islamic, we know little about the relationships between and amongst Islamic humanitarian law, Western (treaty-based) humanitarian law, and the rhetoric and behavior of Islamic armed groups. Our legal analysis suggests that, while there is a great deal of overlap between Western and Islamic humanitarian law, this overlap is not perfect. Our empirical analysis, which focuses on both the words and behaviors of Islamic armed groups, suggests similarly mixed results. Specifically, we find that, on average, Islamic armed groups do not appear to be more or less compliant with Western or Islamic humanitarian law than non-Islamic armed groups when it comes to civilian targeting and child soldiering. While they often appeal to Islamic humanitarian law, Islamic armed groups appear to be bound by similar political and military – rather than religious or legal – constraints to non-Islamic armed groups.