This document discusses the use of mobile phones for healthcare and public health initiatives, known as mHealth. It details the 12 main clusters of mHealth applications, including patient communication, access to web-based resources, point-of-care tools, disease management, education, and more. The document examines how widespread mobile phone ownership is globally and among different populations. It argues that mHealth offers opportunities to improve individual and population health as well as address disparities, but that barriers still exist that must be overcome for successful initiatives.