The interaction between the fungus Leptosphaeria maculans and oilseed rape (Brassica napus) is becoming an excellent model system for studying genetics of host-pathogen interactions. Leptosphaeria maculans causes phoma stem canker (blackleg) on oilseed rape and other Brassica crops worldwide. Recently, application of molecular techniques has led to increased understanding of the genetics of this hemibiotrophic interaction. The complete sequences of the genomes of L. maculans and B. rapa (comprising the Brassica A genome) will be available soon. This will provide new opportunities to investigate basic metabolic pathways in the host and the pathogen, and detailed knowledge of the disease process. Worldwide, the major strategy for control of phoma stem canker is the use of cultivars with resistance to L. maculans.