Plant mycobiome represents a diverse array of plant-associated communities of endophytic and epiphytic fungi. These communities fundamentally affect plant health, development, adaptation, and communication with the surrounding ecosystem. Furthermore, they have key roles in the establishment, diversification, productivity, and sustainability of different natural ecosystems. However, some of these communities are pathogenic for the plant itself or dangerous for the consumers, due to the production of mycotoxins. In other words, plant mycobiome represents two faces of a coin. This book aimed to explore contributions of the plant mycobiome in plant-environment interactions from different perspectives. Chapters of this book address numerous themes covering the recent advances in roles, diversity, and dynamics of these fungi as biocontrol agents, biofertilizers, growth promoters, and their secondary metabolites in the area of crop improvement for sustainability and biotechnology, as well as the plant pathogenic and toxigenic fungi. This book will be useful to postgraduate students, botanists, mycologists, ecologists, plant pathologists, and physiologists.