The phytosociology and ecology of puna vegetation in twelve localities at an altitude of 3750–4500 m in northern Moquegua (south Peru) have been studied. The study area has a pluviseasonal climate with summer rainfall. Using TWINSPAN, Detrended Correspondence Analysis and Farthest Neighbor Clustering, 157 phytosociological relevés were analyzed. For each community, the syntaxonomy, floristic diversity and relation with environmental variables are discussed. 210 vascular plant species belonging to 131 genera and 52 families were recorded. Three main vegetation types were distinguished: 1. chasmophyte vegetation composed of a great diversity of shrubs, dwarf shrubs, ferns and annuals, 2. Puya raimondii stands characterized by considerable species richness in shrubs, grasses and herbs, and 3. extensive puna grasslands influenced by grazing. The zonal vegetation of the supratropical and orotropical bioclimatic belts was represented by two phytosociological classes: Argyrochosmetea niveae (chasmophytes) and Calamagrostietea vicunarum (Puya raimondii and puna grasslands). Within the Argyrochosmetea niveae and Salpichroetalia glandulosae, the new alliances Argyrochosmo niveae-Neowerdermannion peruvianae and Hypochaerido mucidae-Loricarion graveolentis were distinguished, including six associations consisting of steep rock and crevice shrublands on lithosols. Within the Azorello compactae-Festucion orthophyllae (Calamagrostietea vicunarum) two associations with four subassociations and two communities were distinguished comprising grasslands and Puya raimondii stands. One association was described in the Calamagrostion minimae. The puna vegetation of Moquegua hosts rare, endangered and/or protected plant species in Peru. The vulnerability of the flora and vegetation in the mountains of Moquegua is briefly discussed.