Trichotillomania is a psychiatric disorder characterized by recurrent hair pulling, leading to hair loss and functional impairment. This chapter reviews the phenomenology and epidemiology of trichotillomania, and considers its relationship with putative obsessive-compulsive spectrum conditions and other body-focused repetitive behaviors. Salient animal models of the disorder, along with findings in human patients using neuroimaging and cognitive probes, are summarized. A brain-based model of trichotillomania is formulated, focusing on affect dysregulation, addiction, and impulse dyscontrol. Finally, the chapter flags cardinal questions for the attention of future clinical and research scrutiny.