Research on the interactions of plants and phytopathogenic fungi has become one of the most interesting and rapidly moving fields in the plant sciences, the findings of which have contributed tremendously to the development of new strategies of plant protection. This book offers insight into the state of present knowledge. Special emphasis is placed on recognition phenomena between plants and fungi, parasitization strategies employed by the phytopathogenic fungi, the action of phytotoxins, the compatibility of pathogens with host plants and the basic resistance of non-host plants as well as cultivar-specific resistance of host plants. Special attention is paid to the gene-for-gene hypothesis for the determination of race-specific resistance, its molecular models and to the nature of race non-specific resistance as well as the population dynamics of plants and the evolution of their basic resistance.