Introduction: The effectiveness of any new technology is typically measured in order to determine whether it successfully achieves equal or superior objectives over what is currently offered. Research in telemental health—in this article mainly referring to telepsychiatry and psychological services—has advanced rapidly since 2003, and a new effectiveness review is needed. Materials and Methods: The authors reviewed the published literature to synthesize information on what is and what is not effective related to telemental health. Terms for the search included, but were not limited to, telepsychiatry, effectiveness, mental health, e-health, videoconferencing, telemedicine, cost, access, and international. Results: Telemental health is effective for diagnosis and assessment across many populations (adult, child, geriatric, and ethnic) and for disorders in many settings (emergency, home health) and appears to be comparable to in-person care. In addition, this review has identified new models of care (i.e., collaborative care, asynchronous, mobile) with equally positive outcomes. Conclusions: Telemental health is effective and increases access to care. Future directions suggest the need for more research on service models, specific disorders, the issues relevant to culture and language, and cost.