Tomato is known to be afflicted by at least 200 different disease-causing organisms from most major pathogen classes – bacteria, fungi (including Oomycota), viruses and nematodes. Despite decades of conventional breeding and selection, there are still a large number of diseases caused by these pathogen classes that make tomato production challenging in various parts of the world. Current advances in tomato genetics and genomics can be combined with conventional plant-breeding methods to introgress the gene of interest and expedite the breeding process. This chapter summarizes the historical aspect of tomato variety development and describes in detail the current status of application of technology towards the development of disease-resistant varieties. The chapter covers tomato diseases caused by bacteria, fungi, viruses and nematodes.