In 2005–2006, the National Park Service’s Northern Colorado Plateau Network received funding to develop a revised checklist of the vascular plant flora of Pipe Spring National Monument. This entailed a thorough review of existing literature, re-examination of specimens from the Pipe Spring National Monument herbarium and other state and national museum collections, and additional field work to corroborate unverified species reports or locate new species. Based on this study, 277 vascular plant taxa have been confirmed or reliably reported as occurring in the monument (215 are known from validated herbarium specimens and 62 from unvouchered literature reports). Another 15 species formerly considered part of the monument flora have now been shown to be falsely reported. The current flora of Pipe Spring National Monument represents 6.5% of the known flora of Arizona and 11% of the flora of northern Arizona and the Arizona Strip. Although no federally listed threatened or endangered species are known from the monument, two occur in the vicinity. Three plant species from Pipe Spring National Monument are currently tracked as species of concern by the State of Arizona’s Natural Heritage Program. Introduced plants make up nearly 21% of the monument flora (58 species), of which only 4 species are considered noxious weeds by the State of Arizona. Further surveys in Pipe Spring National Monument are likely to find additional new species (46 are known from similar habitats outside the monument boundary), especially among late-season flowering, weedy, or wetland taxa. This checklist includes updates from 2011 and 2012.