This handbook is an established text that continues to provide a comprehensive introduction to Mycobacterium avium subsp paratuberculosis (MTP). It will appeal to undergraduates and postgraduate students. This handbook has been fully revised and updated to reflect the many existing new developments and techniques in the field of handling and diagnosis of MTP. One main reason for separation of contents in to theoretical and practical is for better understanding and to create interest among the readers. The authors have presented a well illustrated text which the readers will find interesting as well as informative, with technical details. In keeping with modern teaching, this handbook adopts a functional approach and emphasizes the classification, physiology, pathogenic interaction and practical significance of MTP.