Microbes. Those unassuming and unseen inhabitants, occupying almost every niche on land and sea, have once more been found to have importance far beyond their physical stature. Many scientists are familiar with Thermus aquaticus, a thermophilic microbe that can survive temperatures upwards of 70°C, the source of the first thermostable DNA polymerase, Taq. Microbes related to T. aquaticus even live at the deep-sea hydrothermal vents, often making use of sulfur from these vents as a source of energy. But in the water columns between the deep-sea vents and ocean surface lives an extraordinarily diverse range of interconnected microbial populations that are only now being characterized and understood. More importantly, scientists are uncovering new roles that these microbes play in the ocean carbon cycle and, consequently, in the global climate. This volume seeks to bring together both the historical and the current research on this topic.