This book focuses on viruses of a Vibrio species in order to serve as a model for heterotrophic host- virus interactions in the marine environment. The estimated 10^30 viruses in the ocean, if stretched end to end, would span farther than the nearest 60 galaxies. This massive virioplankton exert significant influence on marine phytoplankton and bacteria. These effects include the reduction of productivity through viral-mediated mortality, the short-circuiting (virus shunt) of organic matter back into the dissolved pool through lysis products, mediating horizontal genetic exchange and lysogenic conversion, and influencing the richness and evenness (i.e.: overall diversity) of host populations. It is the latter category of effects which are centrally addressed in this book: What can the distribution and the diversity of both virus and host populations tell us about the host-virus relationship?