The main purpose of this publication is to give a systematic definition and accurate description of all weeds growing in the USSR and littering all kinds of crops. There are also more detailed descriptions of seeds, fruits and seedlings of weeds, a brief biological description, mainly with regard to reproduction, information on the use of weeds and measures to combat them. In order to facilitate the definition of weed species, the text contains a fairly large number of patterns of both whole plants and fruits, seeds and seedlings.