Hydraulics is a topic of science and engineering dealing with the mechanical properties of liquids. Hydraulics is part of the more general discipline of fluid power. Fluid mechanics provides the theoretical foundation for hydraulics, which focuses on the engineering uses of fluid properties. Hydraulic topics range through most science and engineering disciplines, and cover concepts such as pipe flow, dam design, fluidics and fluid control circuitry, pumps, turbines, hydropower, computational fluid dynamics, flow measurement, river channel behavior and erosion. However if used incorrectly, hydraulic instruments can result in weird occurrences because of the nature of high pressure fluids.

The word "hydraulics" originates from the Greek word ὑδραυλικός (hydraulikos) which in turn originates from ὕδραυλος (hydraulos) meaning water organ which in turn comes from ὕδωρ (hydor, Greek for water) and αὐλός (aulos, meaning pipe).