The Deep Sea Drilling Project (DSDP) was foremost exploratory, and science planning was almost ad hoc, yet DSDP legs maximized geographic coverage and resulted in a global array of drill sites. With the advent of the Ocean Drilling Program (ODP), the approach changed toward hypothesis-driven science. New projects were now considered using a peer-review system that evaluated submitted proposals against a science plan. This plan was based on a survey of the international scientific ocean drilling community designed to establish new science themes, challenges, and priorities. From the mid-1980s through 2003, several long-range guiding documents encouraged studies that supported multiple and evolving themes; these included the Report of the Second Conference on Scientific Ocean Drilling (1987), A Record of Our Changing Planet (1990), and Understanding Our Dynamic Earth through Ocean Drilling (1996). Using such documents to guide proposal submission and peer review was deemed highly successful, so the successor program, the Integrated Ocean Drilling Program (IODP), was guided by a new science plan, Earth, Oceans and Life: Scientific Investigation of the Earth System using Multiple Drilling Platforms and New Technologies, from 2003–2013 (2001). With this plan, the study of microbial life forms in the ocean’s substrate became part of the research portfolio, leading to three themes: The Deep Biosphere and Subseafloor Ocean; Environmental Change, Processes, and Effects; and Solid Earth Cycles and Geodynamics.