The cultivated tomato (Solanum lycopersicum L.) constitutes a major agricultural industry: it is grown worldwide and, in terms of vegetable crop production, is only second to potato. Tomato plants show a wide climatic tolerance and are grown in both tropical and temperate regions around the world. Viral diseases are responsible for heavy yield losses and are one of the reasons that in many locations tomato production has shifted from open-field to protected production. The three most important tomato viruses in terms of production losses are Tomato yellow leaf curl virus (TYLCV), Tomato mosaic virus (ToMV) and Tomato spotted wilt virus (TSWV). This chapter describes the development of genetic resistances to these three viruses in tomato.