Given the ability to use the internet and applications that are both immediately accessible and highly rewarding to users, concern exists regarding the development of excessive and dysregulated smartphone use (also known as ‘smartphone addiction’). This chapter reviews the current state of research on dysregulated smartphone use, identifies gaps in the literature, and outlines future directions for research and practice. Dysregulated smartphone use is associated with a (1) significant loss of control over the behavior, resulting in (2) severe and persistent functional impairment in daily life. The most consistent correlates of dysregulated smartphone use include psychiatric symptoms and poor sleep health. Because there are few longitudinal studies with a rigorous methodology, it is not clear whether the correlates precede, co-occur with, or follow the onset of dysregulated smartphone use. Consistent conceptualization suggests that mental health problems could precede dysregulated smartphone use. Future research should seek to validate psychometrically sound screening instruments for dysregulated smartphone use in children and adolescents. Research on the longitudinal trajectories of dysregulated smartphone use and psychopathology, as well as physical health outcomes, is recommended. Given the high rates of smartphone ownership among children and young adolescents, clarifying how, and for whom, smartphone use interferes with functioning is critical.