Oviposition behavior in phytophagous insects and entomophagous parasitoids is often modified by the presence of conspecific brood (eggs and larvae). Often, females avoid laying eggs on or in hosts bearing brood, a behavior that acts to reduce the level of competition suffered by their offspring. Avoidance of occupied hosts is typically mediated by cues and/or signals associated with brood. In this article, we review the role of Marking Pheromones (MPs) as signals of brood presence in both phytophagous and entomophagous insects. We place information about the function and evolution of MPs in the context of recent theory in the field of animal communication. We highlight the dynamics of host-marking systems and discuss how effects of MPs vary according to factors such as female experience and egg load. We also examine variation in the form and function of MP communication across a variety of insect taxa. While studies of MP communication in phytophagous insects have focused on the underlying behavioral mechanisms and chemistry of MP communication, studies in entomophagous insects have focused on the functional aspects of MPs and their role in ‘decision-making’ in insects. We argue that an approach that incorporates the important contributions of both of these somewhat independent, but complementary areas of research will lead to a more complete understanding of MPs in insects. Finally, we suggest that MP systems are model systems for the study of animal signaling and its evolution.