Comparative Immunology has gained wide acceptance in biology, as an offspring of immunology and an amalgam of immunology and zoology. The prescient experiments of Metchnikoff on phagocytosis in invertebrates during the 19th century served to splinter immunology into its two main components: cellular and humoral. There is much interest in the immune system of invertebrates as representing early models or precursors of the innate system of vertebrates that by contrast possess the innate system as well as the more highly evolved adaptive system. With respect to mechanisms, we think of the invertebrate system as innate, natural, non-specific, nonanticipatory, and non-clonal. Innate immunity operates through leukocytes that are not components of the macrophage T and B interrelationships that characterize vertebrate adaptive immunity that is adaptive, induced, specific, anticipatory, and clonal. This symposium on invertebrate immunology has provided an overview of what is current and crucial to understanding the larger field of comparative immunology. Comparative immunology is now an established field, here since Metchnikoff but officially since about 1977, with a journal (Developmental and Comparative Immunology) (DCI) and an International Society of Developmental and Comparative Immunology (ISDCI). During this short but vigorous history several national, adherent societies have been organized in Japan, Italy and Germany with sporadic interest in a national group in the USA. Nevertheless, comparative immunology is here as vital to zoology in general and to immunology in particular as we delve deeper into unique but also shared characteristics.