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).