Identification of new biochemical compounds from plants or microorganisms is a great target that serves different fields of science. For example in the agricultural field, identification of a new inhibitory compound against a plant pathogen (microorganism, insect, parasitic weed or nematodes) can be used for control of this pathogen by biotechnological means. On other hand, identification of a new antimicrobial agent against human or animal pathogens is also a noble target. Methods for extraction, purification and chemical structure elucidation of both organic and proteineous bio-active compounds against different types of plant or human pathogens, from different sample types (plant, root exudates, microorganisms and algae) are described in detail in this book.This book will be a helpful guide for the researchers in the agricultural, human and animal health and environmental fields.