A bell jar is a piece of glassware with a rounded top and an open bottom. There are a number of uses for bell jars; for example, historically, they have been used to create a vacuum for scientific experimentation. Many scientific supply stores sell bell jars in an assortment of sizes, along with other accessories which may be used along with them, and they can also be purchased through specialty purveyors of glassware.

When used in the laboratory, a bell jar can be fitted over a snug base which will ensure a clean seal. The inside of the bell jar can be turned into a vacuum for the purpose of experimenting with various objects in the vacuum. The clear glass makes the results of the experiment readily visible, and for this reason, bell jars are often used in science classes to demonstrate basic experiments. Most major labs use other, more reliable technology to create vacuums for experimentation.

A bell jar can also be used to protect and display delicate objects, such as heirloom porcelain. Typically, the object on display is mounted to a sturdy base, and the bell jar is lowered onto it. The Victorians were particularly fond of this sort of display, and bell jars can still be seen in very formal or nostalgic households. Using a bell jar is an excellent way to ensure that an object will be admired while it remains out of danger, although issues of sun bleaching can arise.

Some gardeners also use bell jars, to protect delicate plants. When used with outdoor plants, bell jars can minimize frost damage or protect a plant from insects and other predators. Indoors, a bell jar may keep a plant for being mauled by household pets, and it will also help to keep the plant dust free and less susceptible to changes in temperature. Small arrangements of plants under bell jars are sometimes used in decoration as well.

In 1963, Sylvia Plath, a famous American writer, published a novel called The Bell Jar. The title referenced the fact that a bell jar essentially traps something to keep it on display. Plath used the bell jar as a metaphor to talk about the repression of women in American society. The work is considered to be a classic in the roman à clef genre, and it is especially popular with students and authors of psychologically wrought poetry.