Book excerpt: There has been a significant surge of interest in the study of the physiology and biochemistry of plant host-parasite interactions in recent years, as evidenced by the number of research papers currently being published on the subject. The in creased interest is probably based on the evidence that effective management of many plant diseases is, for the most part, contingent upon a clear understanding of the nature of host-parasite interactions. This intensified research effort calls for a greater number of books, such as this one, designed to compile, synthesize, and evaluate widely scattered pieces of information on this subject. The study of host-parasite interactions concerns the struggle between plants and pathogens, which has been incessant throughout their coevolution. Such in teractions are often highly complex. Pathogens have developed sophisticated of fensive systems to parasitize plants, while plants have evolved diversified defen sive strategies to ward off potential pathogens. In certain cases, the outcome of a specific host-parasite interaction seems to depend upon the presence or efficacy of the plant's defense system. A plant may become diseased when a parasite manages to invade it, unhindered by preexisting defense systems and/or without eliciting the plant's induced resistance response(s). Absence of disease may re flect the inability of the invading pathogen to overcome the plant's defense sys tem(s).