In this chapter we examine whether rapists are sexually aroused by coercive, nonconsensual sex. This question is theoretically important because it speaks to a potential sexual motivation underlying rape. It is also clinically important in that it may reveal an important assessment and treatment target. We first revisit and update quantitative reviews of studies that examined the phallometric responses of rapists and other men. We then present new data on the discriminative and diagnostic validity of a phallometric test for rapists. Finally, we discuss methodological and conceptual issues in phallometric assessment and the nature of rapists' sexual interests.