This chapter presents the science behind liquids at rest or hydrostatics. The five hydrostatic principles of hydrostatics are presented and demonstrated with the mathematical relationships including pressure created by a column of water and how the relationship of pressure, height, and density with proper unit conversion is required. Potential energy within a system is also presented to understand the interaction of hydrostatic pressures from elevation and external pressures create potential energy. Common instrumentation to measure hydrostatic pressures is also presented.