A shelf (pl. shelves) is a flat horizontal plane which is used in a home, business, store, or elsewhere to hold items that are being displayed, stored, or offered for sale. It is raised off the ground and usually anchored / supported on it is shorter length sides by brackets. It can also be held up by columns or pillars. A shelf is also known as a counter, ledge, mantel, or rack. Tables designed to be placed against a wall, possibly mounted, are known as console tables, and are similar to individual shelves.

While a case suggests a closed object, bookcases are now very commonly open fronted, and as such are often really no more than a simple series of shelves designed to hold books. Thus, curiously, the bookcase has come full circle from its earliest form as a simple shelf, most commonly integrated in the wall in the manner of early aumbries, where a medieval scribe kept the book or codex he was writing, through its development as one of the largest pieces of furniture ever made, typified by the often enormous cabinets of architectural proportions used from the 17th century to recent times and which may be thought of as the direct ancestors of the modern entertainment center.