Perhaps the most fundamental type of information needed to understand marine geology is sea floor shape. Measurements of depth have come a long way from the 19th century lead line methods. As a result of the widespread use of deep-sea sonar profiling since the mid-20th century, generalized bathymetric maps (e.g., GEBCO, 1980, NOAA-NGDC, 1985) and data bases of the world’s oceans have been produced. Such maps and data bases are primarily based upon compilations of individual trackline sonar profiles. Significant advances in sonar technology over the past three decades have provided new classes of mapping systems capable of collecting more than just an individual trackline profile: multibeam bathymetry and side-scan sonar mapping systems. Additionally, vast improvements have been made in the ability to photograph and directly observe the sea floor, measure the potential field (magnetics and gravity) created by the suboceanic rock, and profile through the sedimentary strata. Remote sensing acoustic, optical, and potential field instrumentation thus play a critical role in determining the nature of the sea floor.