A phytosociological survey based on methods of the Zürich-Montpellier School was carried out in the páramo vegetation of the Cordillera Oriental, Colombia. The study area covers about 10,000 and comprises the páramo between the Nevado de Sumapaz (3°55'N, 4250 m), the Sierra Nevada del Cocuy (6°25'N, 5493 m) and the Páramo del Almorzadero (7°N, 4375 m). The páramo vegetation was studied along various altitudinal transects from the upper forest line (3000-3500 m) up to the lower limit of the snowcap (4800 m). A general description of the study area includes data on geology, geomorphology, soils, climate, flora, phytogeography, morphological characters of the vegetation, fauna and landuse. The evolution and Quaternary history of páramo vegetation and climate is reviewed, incorporating the first data from the Lateglacial and Holocene of the Páramo de Sumapaz. The general altitudinal zonation of the páramo vegetation was studied and is presented for both the dry and the humid side of the Cordillera. The zonal and azonal plant communities are described including their physiognomy, composition and syntaxonomy, habitat and distribution. Eighty five syntaxa from the rank of variant to that of the class are newly described, 17 of which are provisional. The vegetation is not ranked syntaxonomically yet, but described on the basis of preliminary tables. A number of azonal communities, part of them of lesser extent, are described in a similar way. The páramo vegetation is primarily determined by the tropical diurnal high mountain climate. The diversity of the páramo vegetation is related to temperature (altitudinal gradient) and to humidity (dry and wet climate). The presence of zonal bunchgrass páramo, bamboo-bunchgrass páramo or bamboo páramo mainly depends on the complex interrelation between these factors. Finally a synthesis is provided on ecology, morphology and phytogeography of the páramo vegetation of the study area.