Integrated Ocean Drilling Program (IODP) Expedition 301 is part of a multidisciplinary experiment to evaluate formation-scale hydrogeologic properties (transmission and storage) within oceanic crust; determine how fluid pathways are distributed within an active hydrothermal system; establish linkages between fluid circulation, alteration, and geomicrobial processes; and determine relations between seismic and hydrologic anisotropy. During IODP Expedition 301, we will replace two existing subseafloor observatories and install two new observatories, creating a three-dimensional monitoring network. We will also core and sample basaltic upper crust and overlying sediments to assess physical, geochemical, and microbiological conditions and complete a series of downhole experiments (e.g., packer and downhole logging) in basement to assess hydrogeologic properties near the new boreholes. An additional basement hole will be drilled during a later expedition, allowing completion of controlled, long-term, cross-hole testing. Collectively, these operations and experiments will allow us to evaluate the extent to which oceanic crust is connected vertically and horizontally; the influence of these connections on fluid, solute, heat, and microbiological processes; and the importance of scaling on hydrologic properties.