In the main we have followed Sweetman (1936) and Allee et al. (1949) in arriving at the following definitions: =Symbiosis= is the living together in more or less intimate association of organisms of different species; it includes virtually all relationships between cockroaches and other organisms, such as parasitism, predatism, commensalism, and mutualism. Allee et al. (1949) apparently do not include predatism in symbiosis. =Mutualism= is symbiosis in which both members benefit by the association. The smaller partner has commonly been called a symbiont or symbiote by authors. =Commensalism= includes associations in which neither party appears to benefit or be harmed. One partner may live on the surplus food or wastes of the other; shelter and transport may be involved. =Parasitism= is the state of symbiosis in which one of the members feeds upon the other during the whole of either the immature or mature feeding stage; the host is harmed in some way and may be killed. =Predatism= is an association in which one member attacks and feeds upon, or stores as food for its progeny, one or more other organisms; the predator spends less than the immature or mature feeding period on the prey. This category includes a few invertebrates and all the vertebrates that capture, kill, and feed on cockroaches. This association may be divided into interspecies predatism, in which the predator preys upon a different species, and intraspecies predatism (cannibalism) in which the predator preys upon its own species. Although we have attempted to adhere to these definitions throughout this discussion, we realize that in doing so we may have tended to oversimplify complex relations. Some questionable interpretations stem from insufficient knowledge of the basic relationships between cockroaches and their associates. Only further study will clarify these relationships. Some of the problems are discussed below.