The major growth in point-of-care malaria diagnosis over the past decade has been based on immunochromatographic malaria rapid diagnostic tests (mRDTs), which generally detect Plasmodium falciparum via its abundant histidine-rich protein 2 (HRP2). Here, we review the discovery and biology of HRP2, as well as the strengths and weaknesses of HRP2-based diagnosis compared with alternative antigens. We highlight recent studies describing HRP2 deletion in Latin America, Eritrea, and possibly other regions, and the methodological challenges of confirming deletion of the pfhrp2 gene. We also discuss the mechanism of persistent HRP2 positivity after effective antimalarial treatment, along with other emerging HRP2-based applications, including detection of submicroscopic malaria and diagnosis of severe malaria.