The International AIDS Society-USA (IAS-USA) Drug Resistance Mutations Group is a volunteer panel of experts that meets regularly to review and interpret new data on HIV-1 resistance. The focus of the group is to identify mutations associated with clinical resistance to HIV-1. These mutations have been identified by 1 or more of the following criteria: (1) in vitro passage experiments or validation of contribution to resistance by using site-directed mutagenesis; (2) susceptibility testing of laboratory or clinical isolates; (3) genetic sequencing of viruses from patients in whom the drug is failing; (4) correlation studies between genotype at baseline and virologic response in patients exposed to the drug. Drugs that have been approved by the US Food and Drug Administration (FDA) or available through expanded access protocols are included.