The development of drug resistance as well as appearance of undesirable side effects of certain antibiotics has led to the search for new antimicrobial agents mainly from natural source with the goal to discover new chemical structures. Mushrooms are useful, delicious and mysterious members of the biosphere. Because of their taste and fleshy construction, they have been paid the attention by mankind for ages. Today, mushrooms are considered as an alternative food source to provide adequate nutrition to the world's increasing populations. Mushrooms have become attractive as a functional food and as sources for the development of drugs and nutraceuticals, namely for their antioxidant potential. Both fruiting body and the mycelium of mushrooms contain compounds with wide ranging antimicrobial activity and are rich sources of natural antibiotics. In this book you can find in details how to classify the mushrooms, techniques for antimicrobial activity and primary phytochemical screening method. This book is useful for students studying Pharmacology and Applied Sciences also for researchers around the world concerning with drug discovery for resistant microorganisms from natural sources.