Utilizing a sample of homeless street youth, the authors apply Wikström’s situational action theory (SAT) to explaining drug use. The article examines the assertion that morality is the most important factor in explaining crime and that self-control and deterrence are key factors in understanding criminal behavior only at moderate levels of morality. Results reveal that morality has a strong effect on hard but not soft drug use, whereas the impact of deterrence on both forms of behavior is stronger than self-control. The proposed conditioning effects outlined in SAT do not have significant associations with drug use. Implications for the theory and avenues for future research are offered.