水肺潜水（英语：Self-Contained Underwater Breathing Apparatus，缩写：SCUBA），指潜水员自行携带水下呼吸系统所进行的潜水活动，其中有开放式（open-circuit）呼吸系统及封闭式（closed-circuit）呼吸系统，原理都是利用调节器（Regulator）设备把气瓶中的压缩气体转化成可供人体正常呼吸的压力。

开放式呼吸系统相对较简单，亦为现时较多人使用的系统，此种系统供应呼吸用气体给潜水员单次使用并且被排走。封闭式呼吸系统又称循环呼吸器（rebreather），此系统提供可循环使用的供气。潜水员使用供气后，系统会将二氧化碳吸收，并且重新注入适当氧气，再供应给予潜水员。此类系统可提供压缩空气、高氧（Nitrox）或多种混合气体给潜水员使用。使用不同的气体，可以针对不同的潜水时限、深度，以避免减压症。

Scuba diving is a mode of underwater diving in which a scuba diver uses a self-contained underwater breathing apparatus (scuba) to breathe underwater.

Unlike other modes of diving, which rely either on breath-hold or on breathing gas pumped from the surface, scuba divers carry their own source of breathing gas, usually compressed air, allowing them greater freedom of movement than with an air line or diver's umbilical and longer underwater endurance than breath-hold. Scuba equipment may be open circuit, in which exhaled gas is expelled to the surroundings, or a closed or semi-closed circuit rebreather, in which the breathing gas is scrubbed to remove carbon dioxide, and the oxygen used is replenished from a supply of feed gas before being re-breathed.