The systems approach to offshore site investigations is presented and discussed. After considering the flow plan for an offshore investigation and the requirements for bathymetric and geophysical surveys that usually precede a soils investigation, emphasis is placed on describing the composite parts of the drill ship and wireline sampling and in-situ testing systems and the stationary and moveable seabed systems. In the drill ship system, the various methods of reducing or preventing vertical motion of the drill string to improve drilling, sampling, and in-situ testing performance are briefly evaluated. Sensors common to both systems are reviewed, and sensor calibration is briefly discussed. Problems of data management are considered and a new system is presented. A number of special drilling and in-situ methods are examined to complete the systems approach to offshore geotechnical investigations.