This volume contains the proceedings of the Bathsheva de Rothschild Seminar on Innate Immunity, held on October 10-15, 1999, in Zichron Yaakov, Israel. In recent years, scientific attention has focused increasingly on immediate defense mechanisms based on non-clonal recognition of microbial components. These mechanisms constitute the innate immunity arm of the body's defense. Identification of pathogens by these mechanisms primarily involves receptors recognizing sugar moieties of various micro-organisms. This text describes advances in this field, including the implications of the recognition of specific components of the innate immunity arsenal as the main cause of host susceptibility to particular types of infections, and the development of new agents to combat infections using newly identified anti-microbial peptides. There is also coverage of the major themes, such as the role of innate immune responses as a first-line defense against microbial infection and tumor cells; the cellular and molecular basis of the function of cells and molecules involved in innate immunity; the role of innate immunity in the immunocompromised host; and the interactions between innate immunity components and clonal immune response.