Mutation to resistance is more likely to occur to systemic fungicides than to conventional fungicides. The possibilities to obtain systemic fungicides, to which fungi will not readily become resistant, are discussed. A high potential for development of fungicide resistance does, however, not always imply that problems will arise in practice. If fungicide resistance is accompanied with reduced pathogenicity and fitness, the build-up of a resistant population will be hampered or prevented. Of importance are also the type of disease and the selection pressure exerted by the fungicide. The latter may be influenced by the management of fungicide application.