For the past two decades, much effort has been made to understand the complex interactions between lymphocytes and antigen-presenting cells that result in immune responses. Immunologists have identified an extraordinary diversity of cytokines as players in these interactions, some the products of cellular activation which themselves activate surrounding cells. Meanwhile, another community of investigators, interested in how genes turn on, were using lymphocytes as easily cultivated cells with which to study transcriptional regulation from a molecular perspective. Connections between these areas of study, with their quite different technical vocabularies and experimental approaches, were limited. The 64th Annual Cold Spring Harbor Symposium was therefore a particularly imaginative meeting, intended to provoke a dialogue on the nature of the membrane signals and intracytoplasmic events that provoke the generation of immunity. It did. The debate ranged over biochemistry, physiology, and molecular genetics as well as classical cellular immunology, involving over 70 of the world's leading investigators in a discussion described by the summarizer as the best he had ever attended. The book prompted by the meeting contains personal summaries of the contributions these investigators have made to their fields over the years, with reference to their most recently reported data. This volume therefore contains a remarkably fresh and original perspective on an important aspect of immunology that is necessary to understand in order to undertake rational manipulation of immune responses. All laboratories committed to the future of immunology should have this book, as well as investigators in gene regulation seeking a wide-ranging survey of results achieved with lymphocytes.