A bathtub, also known simply as a bath or tub, is a container for holding water in which a person or animal may bathe. Most modern bathtubs are made of thermoformed acrylic, porcelain-enameled steel, fiberglass-reinforced polyester, or porcelain-enameled cast iron. A bathtub is usually placed in a bathroom either as a stand-alone fixture or in conjunction with a shower. Modern bathtubs have overflow and waste drains and may have taps mounted on them. They are usually built-in, but may be free-standing or sometimes sunken. Until recently, most bathtubs were roughly rectangular in shape, but with the advent of acrylic thermoformed baths, more shapes are becoming available. Bathtubs are commonly white in color, although many other colors can be found. The process for enamelling cast iron bathtubs was invented by the Scottish-born American David Dunbar Buick. Older Western bathtubs are usually made of rust-treated steel or iron. For a long time, most bathtubs are rectangular. In recent years, due to the increasing popularity of acrylic heating bathtubs, various shapes of bathtubs have begun to appear. The most common color for bathtubs is white, but there are other shades such as pink. Most bathtubs have a drain level at the bottom and a drain level in the upper part to prevent overflow. Some have the hose installed at the edge of the bathtub.

The clawfoot tub was considered a luxury item in the late 19th century, originally made from cast iron and lined with porcelain. Modern technology has contributed to a drop in the price of clawfoot tubs, which may now be made of fiberglass, acrylic or other modern materials. Clawfoot tubs usually require more water than a standard bathtub, because generally they are larger. While true antique clawfoot tubs are still considered collectible items, new reproduction clawfoot tubs are chosen by remodellers and new home builders and much like the Western-style bathtubs , clawfoot tubs can also include a variety of shower head options. Freestanding tubs have become popular in recent years as a result of larger bathrooms being constructed. Freestanding bathtubs may be made from various materials such as stone resin, cast stone, acrylic, cast iron, fiberglass, porcelain, copper, and cement. A baby bathtub is one used for bathing infants, especially those not yet old enough to sit up on their own. These can be either a small, stand-alone bath that is filled with water from another source, or a device for supporting the baby that is placed in a standard bathtub. Many are designed to allow the baby to recline while keeping its head out of the water. Hot tubs are common heated pools used for relaxation and sometimes for therapy. Hot tubs became popularized in the U.S. during the early hippie era (1967–1980), appearing in films and music.

Bathtub faucets are valves in the bathroom that control the release of liquids or gases. Water for baths, sinks and basins can be provided by separate hot and cold taps; this arrangement is common in older installations, particularly in public washrooms/lavatories and utility rooms/laundries. In kitchens and bathrooms, mixer taps are commonly used. In this case, hot and cold water from the two valves is mixed before reaching the outlet, allowing the water to emerge at any temperature between that of the hot and cold water supplies. Mixer taps were invented by Thomas Campbell of Saint John, New Brunswick, and patented in 1880. For baths and showers, mixer taps frequently incorporate some sort of pressure balancing feature so that the hot/cold mixture ratio will not be affected by transient changes in the pressure of one or other of the supplies. This helps avoid scalding or uncomfortable chilling as other water loads occur (such as the flushing of a toilet). Rather than two separate valves, mixer taps frequently use a single, more complex, valve controlled by a single handle (single handle mixer). The handle moves up and down to control the amount of water flow and from side to side to control the temperature of the water. Especially for baths and showers, the latest designs are thermostatic mixing valves that do this using a built-in thermostat, and can be mechanical or electronic. There are also taps with color LEDs to show the temperature of the water.