A few years ago, a Mexican man in the United States allegedly abused his young stepdaughter by fondling her breasts. Last summer, his ex-wife formally accused him of this crime, and the public defender hired me to serve as an expert witness in the sexual abuse case. The defendant argued that he had not intentionally fondled the girl, and that when this occurred a younger boy—his biological son—was also present in the bed. His lawyer believed that some of his ideas and behaviors concerning bed-sharing behavior were cultural, and that is why she contacted me.1 My task was to establish whether, in fact, in "Mexican culture" such bed-sharing behavior is considered appropriate. As I prepared myself for this endeavor I found that there is a dearth of information about the practical, scholarly, and ethical dilemmas I encountered along the process of serving as an expert witness. The case never made it to trial, as the defendant was eventually offered a plea deal in large part because of my testimony. Nonetheless, I learned valuable lessons throughout the process that will undoubtedly be useful for any cultural anthropologist facing this role.