This book arose out of teaching graduate and undergraduate classes in wildlife diseases. It, in some ways, chronicles my involvement in the inves- gation and diagnosis of diseases in free-ranging wildlife, primarily in western and northern Canada, since the 1960s. It also, perhaps, reflects the devel- ment of wildlife disease study as a discipline. Much of the earlier work in this field was purely descriptive, documenting the occurrence of various diseases in wild animals. I have chosen to retain references to some older and obscure information in this second edition because this body of work provides the foundation for a more analytical approach. The literature on health problems in free-ranging animals is expanding rapidly. I am gratified that the theor- ical and quantitative aspects of wildlife disease are receiving more attention than in the past, and that role of disease as a factor in population biology is being analyzed. My hope for the first edition of this book was that it would serve as an overview of the study of disease in wild animals and of methods that might be used to manage health problem. It was, and is, not intended to be a how-to book or an encyclopedic reference to the literature on disease; rather it is intended as a seed crystal around which the reader can build. The inquiries I have received about a second edition suggest that it has been useful.