Fungi are heterotrophs and are in this respect in competition with other microorganisms. In addition, they are confronted with parasites and predators that use the fungus as substrate. One major strategy of fungi to protect themselves against competitors and fungivores is the production of toxins. These toxins can range from secondary metabolites, to peptides, to whole proteins. This thesis focusses on the identification and characterization of fungal defense effector proteins. A novel family of ribosomally synthesized and post-translationally modified peptides (RiPPs) is presented and several fungal lectins are investigated in regard to their target specificity and toxicity spectrum.