These consolidated guidelines provide guidance on the diagnosis of human immunodeficiency virus (HIV) infection, the care of people living with HIV and the use of antiretroviral (AV) drugs for treating and preventing HIV infection. They are structured along the continuum of HIV testing, care and treatment. Behavioural, structural and biomedical interventions that do not involve the use of AV drugs are not covered in these guidelines. The 2013 consolidation process combines and harmonizes recommendations from a range of WHO guidelines and other documents, including the 2010 guidelines on using antiretroviral therapy (AT) for HIV infection in adults and adolescents, in infants and children and for treating pregnant women living with HIV and preventing HIV infection in infants. Comprehensive guidance is now provided on using AV drugs across age groups and populations of adults, pregnant and breastfeeding women, adolescents, children and key populations. The guidelines also aim to consolidate and update clinical, service delivery and programmatic guidance. The 2013 guidelines reflect important advances in HIV responses during the past three years. Since 2010, new technologies, including CD4 point-of-care testing and new service delivery approaches, allow HIV testing and treatment monitoring to be diversified and decentralized. Simple, safer, once-daily, single-pill AV regimens that are suitable for use in most populations and age groups have become more affordable and more widely available in low- and middle-income countries. Countries are moving towards earlier initiation of triple-drug regimens and simplified programming for the prevention of mother-to-child transmission of HIV (PMTCT) that emphasizes the long-term health of pregnant women and mothers living with HIV and preventing HIV infection among their children. The broader HIV prevention benefits of AV drugs are being recognized: in addition to improving health and prolonging lives, AT prevents the sexual transmission of HIV, while pre-exposure prophylaxis of HIV with AV drugs expands HIV prevention options and post-exposure prophylaxis of HIV continues to play an important role in managing HIV exposure in certain populations and settings, including for those who have been sexually assaulted. Although countries are at different stages of AT coverage and implementing the 2010 WHO guidelines, there is a consistent global trend towards initiating HIV treatment earlier. Consistent with previous WHO guidelines, the 2013 guidelines are based on a public health approach to the further scaling up of AV drugs for treatment and prevention that considers feasibility and effectiveness across a variety of resource-limited settings. The new clinical recommendations in these guidelines promote expanded eligibility for AT with a CD4 threshold for treatment initiation of 500 cells/mm3 or less for adults, adolescents and older children. Priority should be given to individuals with severe or advanced HIV disease and those with CD4 count of 350 cells /mm3 or less. AT is recommended to be initiated regardless of CD4 count for certain populations, including people with active tuberculosis (TB) disease who are living with HIV, people with both HIV and hepatitis B virus (HBV) infection with severe chronic liver disease, HIV-positive partners in serodiscordant couples, pregnant and breastfeeding women and children younger than five years of age. Harmonization of AV regimens for adults and children is recommended whenever possible, with a new, preferred first-line AV regimen. The need to phase out d4T in first-line AV regimens for adults and adolescents is being reinforced.