Plants are source of almost all basic things require for human being as they synthesis millions of different chemicals in their life cycle. Since discovery of Penicillin, use of antibiotics increased rapidly but due to indiscriminate use of antibiotics number of pathogens (both plants and animal) developed resistance against particular antibiotics which become inefficient. Therefore it is need of hour to search antibiotics from plants instead of microorganism are referred to as antimicrobial agents. This book, therefore provide way for searching antimicrobial agents from plants to control plant as well as animal pathogenic bacteria and fungi in agricultural and medical fields. It guide for primary screening, phytochemical analyses, separation, isolation and purification of active compounds from plants; their mode of action on pathogens while the factors which affect the antimicrobial activity of pure as well as crude extracts also discussed with experiments.