Current knowledge relevant to the understanding of thyroid autoimmunity is summarized in this book. Some of the world’s leading scientists in this field review recent data from four subject areas: immunogenetics, thyroid peroxidase as an antigen, environmental factors, and cytokines. Much ongoing and as yet unpublished work is described, especially in the discussion included after each article. This information is of particular interest since the body of knowledge in these fields is growing very rapidly. The book is based on a workshop in which researchers from 13 countries took part. One major aim was to raise controversial points and to develop ideas for their potential solution. At the workshop it became apparent that a great deal of the information given in textbooks is outdated. This is an important update for researchers who are interested in the above topics and in understanding the etiology and pathogenesis of thyroid autoimmunity.