Immersive virtual environments (IVEs) are systems comprised of digital devices that simulate multiple layers of sensory information so that users experience sight, sound, and even touch like they do in the physical world. Users are typically represented in these environments in the form of virtual humans and may interact with other virtual representations such as health-care providers, coaches, future selves, or treatment stimuli (e.g., phobia triggers, such as crowds of people or spiders). These virtual representations can be controlled by humans (avatars) or computers algorithms (agents). Embodying avatars and interacting with agents, patients can experience sensory-rich simulations in the virtual world that may be difficult or even impossible to experience in the physical world but are sufficiently real to influence health attitudes and behaviors. Avatars and agents are infinitely customizable to tailor virtual experiences at the individual level, and IVEs are able to transcend the spatial and temporal boundaries of the physical world. Although still preliminary, a growing number of studies demonstrate IVEs’ potential as a health promotion and therapy tool, complementing and enhancing current treatment regimens. Attempts to incorporate IVEs into treatments and intervention programs have been made in a number of areas, including physical activity, nutrition, rehabilitation, exposure therapy, and autism spectrum disorders. Although further development and research is necessary, the increasing availability of consumer-grade IVE systems may allow clinicians and patients to consider IVE treatment as a routine part of their regimen in the near future.