This volume summarizes recent advances in our understanding of the mechanisms that produce successful symbiotic partnerships involving microorganisms. It begins with a basic introduction to the nature of and mechanistic benefits derived from symbiotic associations. Taking that background knowledge as the starting point, the next sections include chapters that examine representative examples of coevolutionary associations that have developed between species of microbes, as well as associations between microbes and plants. The authors conclude with a section covering a broad range of associations between microbes and invertebrate animals, in which they discuss the spectrum of hosts, with examples ranging from bryozoans and corals to nematodes, arthropods, and cephalopods. Join the authors on this journey of understanding!