An endophyte is an endosymbiont, which may be a bacterium or a fungus that lives within a plant for at least a part of its life cycle without causing any apparent disease. Fungal endophytes are quite common and highly diverse microorganisms. They may improve host plant's growth and nutrient acquisition along with enhancing the ability of the plants to tolerate abiotic stresses. These endophytes also help in reducing the biotic stress faced by plants by increasing their pathogen resistance. Endophytes can be transmitted either vertically or horizontally. There are two major classifications of endophytes, namely, systemic and non-systemic endophytes, and clavicipitaceous and non-clavicipitaceous endophytes. This book provides a detailed explanation of the significance of fungal endophytes in plants. A number of latest researches have also been included to keep the readers updated with the global concepts in this area of study. The book is appropriate for students seeking detailed information in this area as well as for experts.