Chapter 13 is a more detailed examination of current offshore turbine foundations including fixed-base and floating platforms. The former category includes gravity caissons, monopiles, and jackets, with the comparative advantages of each type assessed in regard to water depth and wind turbine size. Weight comparisons are made for of installed arrays. The monopile is described in detail, including review of transition piece integrity, and analysis of seabed reaction. The Winkler p-y analysis method is described, with extreme load results given for a monopile at Horns Rev 1. A review of jacket foundations includes description of pin pile and suction bucket anchors. The section concludes with details of less common fixed foundation types. The section on floating foundations begins with a general stability analysis for free-floating platforms, with formulae derived for static pitch/roll stiffness and frequency. Spar buoy, semisubmersible, and TLP platforms are described, and experimental measurements for the Hywind spar buoy are presented. The chapter concludes with description and analysis of catenary mooring systems, with equations given for horizontal mooring tension and stiffness.