A kit lens is a "starter" lens which can be sold with an interchangeable-lens camera such as a single-lens reflex camera. It is generally an inexpensive lens priced at the lowest end of the manufacturer's range so as to not add much to a camera kit's price. The kit consists of the camera body, the lens, and various accessories usually necessary to get started in SLR photography. A kit lens can be sold by itself outside of a kit, particularly the ones that are moderately expensive; for instance a kit lens included in a prosumer SLR kit is often marketed as an upgrade lens for a consumer SLR. In addition, retailers often have promotions of standalone low-end SLR bodies without the lens, or a package that bundles the SLR body with one or two more expensive lenses.

Originally kit lenses were of normal focal length; more recently kit lenses tend to be inexpensive zoom lenses that range from medium wide angle to mid telephoto for added versatility. Prime lenses are generally faster (smaller f-number) than comparably priced zoom lenses, so the change to zoom lenses means that recent kit lenses are usually also slower (higher f-number). However, in most cases the inclusion of an inexpensive zoom lens is to maintain a low entry price and maximize usability for the beginner photographer. More expensive camera bodies are often paired with a likewise more expensive, thus possibly faster, lens.

Originally high end SLRs were always sold body-only without a lens as most buyers were experienced users who already had lenses. Today however this is not always the case and even high end SLRs can be purchased with a lens, albeit an appropriately higher-quality lens. In these cases the typically uncomplimentary term "kit lens' is somewhat of a misnomer. Sometimes the lens is added by the retailer at a reduced price over separate body+lens pricing.