An economically important disease of barley that causes significant yield and quality losses is net blotch caused by the necrotrophic fungal pathogen Pyrenophora teres. To reduce the impact of net blotch the research community is engaging in basic and applied research to enhance genetic resistances, as it is the most economic and sustainable management strategy. Durable resistance against P. teres will be a major achievement towards the goal of developing widely adapted barley varieties that have high yields and quality across dynamic environments. This chapter focuses on a thorough review of the latest knowledge of both host resistance/susceptibility and pathogen virulence/avirulence in this important pathosystem, and the implications this knowledge will have on deploying sustainable resistances to this destructive pathogen of barley.