Since the publication of the first edition of "The Mycota Vol. V – Plant Relationships" in 1997, tremendous advances in fungal molecular biology and biochemistry have taken place; and both light and electron microscopical techniques have improved considerably. These new insights led to a better understanding of the relationships between fungi and plants; and a completely revised new edition of Plant Relationships could be produced, providing an up-to-date overview on mutualistic and pathogenic interactions.