The marine subseafloor biosphere is estimated to hold 1/10th to 1/3rd of Earth's microbial biomass. Studies done via scientific ocean drilling, from both the Ocean Drilling Program and Integrated Ocean Drilling Program, have explored the microbial inhabitants of deep sea sediments. Little is known about these subsurface microbes, however, initial sequencing surveys are revealing patterns of microbial diversity that relate to chemical and physical changes of deep sediments. This talk will explore the patterns of bacterial and archaeal diversity revealed by 16S rRNA clone libraries and also massive pyrosequencing tagged amplicons. The relationship of microbial taxa with geochemical regimes will be explored. While many of the subsurface microorganisms are uncultured, and their metabolisms unknown, groups have been found that correlate with geochemical regimes. New data from recent cruises will be explored.