The purpose of this working paper is to revise and update the antiretroviral (ARV) priorities of the Medicines Patent Pool (MPP) taking into consideration recent developments in the clinical, market and intellectual property landscape for different ARVs. As part of its mandate, MPP assigns greater priority to in-licensing HIV medicines that are most important from a clinical perspective and for which there is significant intellectual property in low- and middleincome countries (LMICs). The focus is on ARVs that are already on the market as well as ARVs that are currently in late-stage clinical development, defined as those that are already in Phase III. MPP publishes its prioritization report on an annual basis. The present working paper is the fourth edition.