Since the influenza virus was first isolated in the laboratory some 70 years ago, the disease has been the subject of intense study, and our knowledge has escalated as the newer techniques of medicine and science have made further advances possible. At the present time, our information of the disease and the virus that causes it is probably more detailed than for any other virus infection, perhaps excluding the human immunodeficiency virus. The subject of influenza divides itself into a number of specialities, and such is the pace of research and the depth of our knowledge, that workers in one area may have little understanding of the advances made in others. This volume of Perspectives in Medical Virology has enlisted twelve internationally recognised researchers on specific aspects on the subject of influenza to write a summary of the important developments in the past and offer their views on the problems that remain to be addressed. It is hoped that their emphasis, reservations and projections are of value to future research, and offer directions for a better understanding of the virus, the disease it causes, the production of vaccines and the development of therapeutic agents so that at some date in the future this infection can be brought under control.