WHO guidelines for ART for HIV infection in adults and adolescents were originally published in 2002, and were revised in 2003 and 2006. New evidence has emerged on when to initiate ART, optimal ART regimens, the management of HIV coinfection with tuberculosis and chronic viral hepatitis, and the management of ART failure. This guideline provide evidence-based recommendations outlining a public health approach to the delivery of ART for adults and adolescents, with a focus on settings with limited health systems capacity and resources. To identify the most potent, effective and feasible first-line, second-line and subsequent treatment regimens as components of expanded national responses for HIV care. And to develop recommendations applicable to the majority of populations regarding the optimal timing of ART initiation, preferred first-line and second-line ARV regimens and improved criteria for ART switching, and to introduce the concept of third-line ART regimens.