This book describes about endophytic fungi and their antagonistic and plant growth promoting activity. Fungal endophytes can colonize internal plant tissues without causing apparent harm to their host plant. In modern agriculture, pesticide application is still an invaluable and effective method to control plant diseases. Use of agrochemicals is falling into disfavor because of environmental pollution and detrimental effects on a variety of non target organisms; potential use of microbes based biocontrol agents as replacement or supplements for agrochemicals has been addressed in many recent reports. In that context, we isolated and identified fungal endophytes from living symptomless tissues of eight different medicinal plants in Korea, investigated antifungal activity against seven plant pathogenic fungi in vitro and evaluated in vivo the selected twelve plant growth promoting fungi for growth enhancement of cucumber, tomato and pepper in the green house condition.