Plant diseases caused by pathogens threaten crop production worldwide. One of the approaches to combat pathogens is to improve the plant’s own immunity, a strategy that requires detailed insight into the mechanisms underlying immunity. When plant cells are attacked by pathogens, their immune system is rapidly activated. One of the activated defence responses is a local and precise secretion of antimicrobial compounds and cell wall material at the site of attempted penetration. This requires polarized exocytosis. The central goal of this thesis was to understand polarized exocytosis in plant cells that are locally triggered by attack of a filamentous plant pathogen. We focused on the role of the exocyst complex during this process. The exocyst complex is a conserved multiprotein complex that facilitates one of the final steps of exocytosis. The research described in this thesis demonstrates the power of a multidisciplinary approach for unravelling plant-pathogen interactions. The data obtained by combining phytopathological and cell biological approaches show that the exocyst complex plays an important role in plant immunity against different unrelated pathogens and that exocyst subunits are recruited to sites of pathogen infection where they likely facilitate defence-related exocytosis to halt pathogen penetration.