In this dissertation, I examine whether members of radical environmental and animal rights groups are deterred by legal sanctions, morality, both, or neither. From a rational choice framework, I hypothesize that members of these groups weigh costs and benefits and act based on expected utility. I measure an increase in costs through three federal sentencing acts targeted at reducing the criminal behavior of these groups and hypothesize that this legislation decreased the total, serious, and ideologically-specific activity of extremists. I also contend that two terrorist events, the nearly fatal tree-spiking of George Alexander and the assassination of Hyram Kitchen, also increased the costs of criminal conduct for members of radical eco-groups. I evaluate interviews with twenty-five activists and analyze a database of 1056 incidents through both time-series and series hazard modeling. The interviews yield support for the rational choice perspective, particularly in regards to micro-level considerations of legal sanctions and morality. My quantitative findings indicate that the legislation was influential, albeit varying in direction by the method employed. Specifically, the time-series models yield significant increases in the frequency of criminal conduct after the legislation, while the series hazard analyses demonstrate a decrease in the hazard of an attack. I also find that the two major terrorist events did not significantly impact the criminal conduct of these groups. I conclude that members of radical environmental and animal rights groups are rational actors whom consider the moral evaluation of a given act and are susceptible to an increase in costs as measured through legislative efforts, but not as operationalized as a response to high profile attacks.