This publication contains the proceedings of a Seminar on 'The Mucosal Immune System' held by the Commission of the European Communities (CEC) at the University of Bristol. School of Veterinary Science. Langford. Bristol on September 9th - 11th. 1960. The seminar formed part of the CEC programme of co-ordinated agricultural research on Protection of the Young Animal against Perinatal Disease and was organised by Professor F.J. Bourne and his colleagues Dr. T.J. Newby and Dr. C.R. Stokes. The Proceedings were edited by the organisers assisted by Janssen Services. 33a High Street. Chislehurst. Kent and provide an authoritative and up-to-date account of this rapidly moving research area. Serious economic loss from diseases of mucosal surfaces - particularly the enteric and respiratory tracts - occurs in young farm animals throughout the EEC. Protection against these diseases is based on an understanding of their epidemiology including host defence mechanisms. Mucosal vaccines have in the main given disappointing field results with. however. some notable exceptions. This seminar rationalises methods used to stimulate mucosal immune defence and indicates likely areas for future research and development. The CEC wishes to thank the organisers and the participants who con- tributed to the success of the seminar. OPENING SESSION Chairman F.J. Bourne 3 OPENING REMARKS F.J. Bourne On behalf of the University of Bristol and the European Economic Community my colleagues and I welcome you to the Langford Veterinary School.