Classic study of fluid mechanics concentrates on the flow of a single homogeneous phase. This chapter considers fluids in such an equilibrium state. For fluids in equilibrium, the only internal stresses acting will be normal forces, since the shear stresses depend on velocity gradients, and all such gradients, by the definition of equilibrium, are zero. The chapter assumes the reader is familiar with elementary Cartesian tensor analysis and the associated subscript notation and conventions. The hydrostatic pressure variation may be employed to measure pressure differences in terms of heights of liquid columns—such devices are called manometers and are commonly used in wind tunnels and a host of other applications and devices. The same principles used to compute hydrostatic forces can be used to calculate the net pressure force acting on completely submerged or floating bodies. The stability problem is more complicated for floating bodies because as the body rotates the location of the center of buoyancy may change.