The author summarizes evidence that various biological factors are associated with criminal behavior. The theory presented, called the "evolutionary neuroandrogenic theory," focuses on explaining violent and property offenses. Two main propositions form the core of the theory. One proposition asserts that aggressive and acquisitive criminal behavior evolved as an aspect of human reproduction, especially among males. The second proposition links the probability of aggressive and acquisitive criminal behavior to neurochemistry, notably gender-related hormones that promote "competitive/victimizing" behavior. In theorizing that males are more biologically prone to criminal behavior than females, the assumption is that this gender difference in behavior must be related to the one chromosome that males and females do not share, i.e., the Y-chromosome. The features of the Y-chromosome are discussed in detail, with attention to the role of testosterone in promoting competitive/victimizing behavior related to brain functioning. Other biological factors discussed in relation to criminal behavior are mesomorphy, maternal smoking during pregnancy, hypoglycemia, epilepsy, skin conductivity, resting heart and pulse rates, cortisol, serotonin, monoamine oxidase, and brain waves and low P300 amplitude. Overall, the proposed theory is intended to help move criminology beyond strictly social environmental theories toward a new, more comprehensive paradigm that envisions behavior as stemming from the interaction among biological factors rooted in evolutionary history, learning, and social environmental factors. 1 table, 2 figures,and 112 references