This issue of Current Topics in Microbiology and Immunology records the proceedings of a Workshop on the Immunology of Sili cones held at the Natcher Conference Center, National Institutes of Health, Bethesda, Maryland, March 13 and 14, 1995. A large num ber of investigators from North America and Europe met to discuss available data on how the immune system responds to silicones and related materials. Some aspects of this field are controversial. Nonetheless, the meeting was marked by a civil and open ex change of scientific information and divergent interpretations, re flecting the traditions of scientific communication. Each invited participant was asked to submit an article sum marizing his/her presentation. Most of the papers are published as submitted, with only editorial changes to conform with the guide lines given to each contributor or revisions to clarify aspects of the paper. The papers should not be regarded as peer-reviewed publi cations. This preface will attempt to outline some of the immu nological areas of investigation relating to silicones.