Fluidics, or fluidic logic, is the use of a fluid to perform analog or digital operations similar to those performed with electronics.

The physical basis of fluidics is pneumatics and hydraulics, based on the theoretical foundation of fluid dynamics. The term fluidics is normally used when devices have no moving parts, so ordinary hydraulic components such as hydraulic cylinders and spool valves are not considered or referred to as fluidic devices.

A jet of fluid can be deflected by a weaker jet striking it at the side. This provides nonlinear amplification, similar to the transistor used in electronic digital logic. It is used mostly in environments where electronic digital logic would be unreliable, as in systems exposed to high levels of electromagnetic interference or ionizing radiation.

Nanotechnology considers fluidics as one of its instruments. In this domain, effects such as fluid–solid and fluid–fluid interface forces are often highly significant. Fluidics have also been used for military applications.

In 1920, Nikola Tesla patented a valvular conduit or Tesla valve that works as a fluidic diode. It was a leaky diode, i.e. the reverse flow is non-zero for any applied pressure difference. Tesla's valve also had non-linear response, as its diodicity had frequency dependence. It could be used in fluid circuits, such as a full-wave rectifier, to convert AC to DC. In 1957, Billy M. Horton of the Harry Diamond Laboratories (which later became a part of the Army Research Laboratory) first came up with the idea for the fluidic amplifier when he realized that he could redirect the direction of flue gases using a small bellows. He proposed a theory on stream interaction, stating that one can achieve amplification by deflecting a stream of fluid with a different stream of fluid. In 1959, Horton and his associates, Dr. R. E. Bowles and Ray Warren, constructed a family of working vortex amplifiers out of soap, linoleum, and wood. Their published result caught the attention of several major industries and created a surge of interest in applying fluidics (then called fluid amplification) to sophisticated control systems, which lasted throughout the 1960s. Horton is credited for developing the first fluid amplifier control device and launching the field of fluidics. In 1961, Horton, Warren, and Bowles were among the 27 recipients to receive the first Army Research and Development Achievement Award for developing the fluid amplifier control device.

Logic gates can be built that use water instead of electricity to power the gating function. These are reliant on being positioned in one orientation to perform correctly. An OR gate is simply two pipes being merged, and a NOT gate (inverter) consists of "A" deflecting a supply stream to produce Ā. The AND and XOR gates are sketched in the diagram. An inverter could also be implemented with the XOR gate, as A XOR 1 = Ā.

Another kind of fluidic logic is bubble logic. Bubble logic gates conserve the number of bits entering and exiting the device, because bubbles are neither produced nor destroyed in the logic operation, analogous to billiard-ball computer gates.

In a fluidic amplifier, a fluid supply, which may be air, water, or hydraulic fluid, enters at the bottom. Pressure applied to the control ports C₁ or C₂ deflects the stream, so that it exits via either port O₁ or O₂. The stream entering the control ports may be much weaker than the stream being deflected, so the device has gain.