•The manuscript is on the fundamental mechanisms that shape biotrophic interactions.•Biotrophic model organisms Cladosporium fulvum and Ustilago maydis are highlighted.•Limited number of host proteins (hubs) is addressed by unrelated pathogens.•Intracellular pathogens address more targets compared to apoplastic interactions. Filamentous plant pathogens that establish biotrophic interactions need to avoid plant immune responses. Recent findings from different pathosystems suggest that sufficient suppression of host immunity is based on the modulation of a rather limited number of host targets. Microbial strategies to target host physiology dependent on the duration of biotrophy, the style of host tissue colonization and the degree of interference with plant development. In this article, we present current concepts in biotrophic virulence strategies and discuss mechanisms of pathogen adaptation and effector specialization.