There is an increasing trend for scientists to seek “objective” measurements of sexual desire by taking bodily measurements (using technologies such as penile and vaginal plethysmographs, skin flush measures, pupil dilation, and so on). These technologies have specifically been created in order to avoid “subjective” reports of behaviors and emotions. Since it is hard to imagine something more subjective than sexual desire, Rebecca Jordan-Young became intrigued with the attempt to devise measures that avoid, and even contradict, subjective reports of desire, and asked the question: Why do it? What is the point, and what are the stakes? What contexts and kinds of sexual subjects do scientists have in mind when they devise “objective” measures of desire? What do scientists do when different physical measures fail to agree? What notions of body-mind-self relations are invoked by demanding physical evidence of desires—both in a general sense and in terms of the specific form of bodily evidence that is sought? In addition to specific, socially important, implications for understanding sexual nature and sexual rights, sexual measurement technologies raise more general questions about both the ontological status of subjective phenomena and the possibility that subjectivity can yield scientifically valid evidence.