This book is intended for diagnosticians and poultry veterinarians to aid in the identification and control of immunosuppressive diseases. The goal of this work is to present the reader with the most common diseases that can produce immunosuppression in poultry, provide guidance for the diagnosis of immunosuppressive diseases, and examine the challenges that a diagnostician may face in confirming a diagnosis of immunosuppression. It is the aim of the authors to also emphasize those areas that require more research for a proper diagnosis and control of immunosuppressive diseases. This work features an extensive collection of color photographs depicting the gross and microscopic images and the text provides background information and practical tips in identifying immunosuppression in poultry under laboratory and field conditions. Aim and scope of the book This work is unique in that its entire focus is on immunosuppressive diseases in poultry and will be a reference for all poultry health personnel.