This study presents global 3-D electrical conductivity models of the world ocean and marine sediments. Electrical conductivity of the ocean was calculated by invoking the Equation of State of Seawater (TEOS-10) with temperature and salinity data retrieved from the World Ocean Atlas and a series of high-resolution regional ocean climatology data sets. The resolution of the ocean conductivity atlas varies between 0.urn:x-wiley:15252027:media:ggge22631:ggge22631-math-0001 and 0.urn:x-wiley:15252027:media:ggge22631:ggge22631-math-0002 globally. The conductivity of marine sediments was estimated by using compaction and thermal gradient models constrained by real observations on a 5-arc-minute global marine sediment thickness grid. I present numerical simulations of electromagnetic (EM) induction responses that demonstrate a significant effect of 3-D electrical conductivity of the ocean and marine sediments on EM responses for a broad range of frequencies. I show that both marine and land-based surveys designed for subsurface conductivity imaging or Space Weather modeling will benefit from inclusion of more realistic conductivity models of the ocean and seabed sediments.ISSN:1525-202