In this dissertation, I investigate the causes of differences in the use of suicide terror by non-state armed groups, including magnitude of use, targeting decisions, and how reliant groups are on suicide attacks. I develop and test the propositions that the age of groups and the capability of the state military they face significantly impact the scale of use and targeting selection of their suicide attacks. Older groups are predicted to carry out a decreased number of suicide attacks in comparison with younger groups, but increase their focus on attacking hard targets and decrease their focus on attacking soft targets, due to older groups being more likely to possess skilled terror operatives and to follow traditional guerrilla warfare practices. Groups that began using suicide terror later in their existence are predicted to carry out less suicide attacks than groups that adopt the tactic earlier in their histories, due to organizations having increased reliance on established practices and procedures. Groups fighting strong state militaries are predicted to carry out more suicide attacks, a higher proportion of attacks on soft targets, and be more reliant on suicide terror than are groups fighting weak militaries, as increased military pressure on groups decreases the effectiveness of their individual attacks, reduces their ability to train skilled operatives, and increases their desperation and incentive to use unconventional tactics. I conduct a quantitative analysis of 140 groups from 1998-2012 and find that older groups and groups that adopt suicide terror later in their existence carry out less suicide attacks than younger groups and groups that adopt suicide terror earlier in their histories. I also find that groups respond to increases in state military personnel by carrying out more suicide attacks overall, a higher proportion of suicide attacks against soft targets, a lower proportion against hard targets, and by becoming more reliant on suicide terror. These dynamics are also illustrated in depth through case study analysis of suicide terror campaigns by the Liberation Tigers of Tamil Eelam (LTTE) and Al-Qaeda in Iraq (AQI)/Islamic State of Iraq and the Levant (ISIL), which represent two distinct models of suicide terror.