The paper presents results of investigations of weed vegetation conducted in crop fields, in Tajikistan (Middle Asia) - one of the world cradles of the weed flora. The study has been based on 299 phytosociological relevés obtained in various geobotanical regions of the country in 2009-2012. In the examined vegetation patches 469 vascular plant species were noted. Many of the recorded species are widespread weeds. However, there were also some rare and endemics taxa (e.g. Prangos pabularia, P. saraw-schanica and Thlaspidium thlaspi) observed in the sample plots. The collected material presents probably, the majority of the variability among the weed communities of crop cultivations in the Middle Asia. As a result of numerical analyses, 4 associations were distinguished: Eremodauco lehmannii-Lagonychietum farcti, Vicietum hyrcanico-peregrinae, Asperugo-Cannabietum ruderalis and Lathyretum sativi. All of them are new to science. The main factors determining the species composition of classified associations seem to be the climate conditions, soil type and elevation above sea level. Within Vicietum hyrcanico-peregrinae, two subassociations (garhadioletosum angulosi and anchusetosum italicae) have been distinguished. The species composition of the Middle Asian segetal communities makes it necessary to distinguish a new order: Turgenio latifoliae-Roemerietalia refractae with 3 alliances: Lathyrion sativi, Cirsion incani and Aveno trichophyllae-Euphorbion falcatae within the Stellarietea mediae class.