A bath tub is a plumbing fixture used for bathing. Most modern bathtubs are made of acrylic or fibreglass, but alternatives are available in the form of porcelain-coated steel or increasingly wood. Older western bathtubs are usually made of galvanized steel or iron. Traditional Japanese bathtubs were usually of a wooden construction.

Until recently, most bathtubs were roughly rectangular in shape but with the advent of acrylic thermoformed baths, more and more shapes are becoming available. Bathtubs are typically white in colour although many other colours can be found.

Modern bathtubs encompass an overflow and waste and may or may not have taps mounted on them. They may be built-in or freestanding or sometimes sunken/drop-in.

The issues of depth and intended use are what separates a bathtub from a hot tub or other recreational bathing facilities. A bathtub is usually placed in a bathroom either as a stand-alone fixture or in conjunction with a shower.