The present textbook includes some papers interested in the twospotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae) associated with some field crops e. g. cotton, maize and soybean during last five years in Egypt. These investigations studied ecology,biochemical, control of T. urticae and relationships between mites and host plants.Such included studies could get some knowledge about damage and behaviour of T. urticae and attempts to reduce losses and hazardous of this pest.