Detection of acute HIV infection is important to public health because this stage is one of high infectiousness and appears to account for a disproportionate amount of HIV transmission. Newer technologies in HIV testing, including third-generation enzyme immunoassays (EIAs) that detect anti-HIV IgM and IgG antibodies, fourth-generation combination EIAs that detect both anti-HIV antibodies and HIV p24 antigen, and nucleic acid-based testing for HIV RNA, have markedly reduced the interval between infection and detection of infection. Rapid diagnostic tests including assays for IgG and IgM anti-HIV antibodies have high sensitivity and specificity. The availability and wide use of these newer technologies have motivated review of recommended HIV testing algorithms. Individuals' knowledge of their HIV serostatus contributes to reducing transmission risk behaviors. Thus, widespread testing, facilitated by newer technology, allows more individuals to know their serostatus and is the first step in any successful effort to curb the incidence of HIV infection. This article summarizes a lecture by Demetre Daskalakis, MD, at the New York City IAS-USA continuing medical education program held in November 2009 and re-presented in December 2010.