A book is a set or collection of written, printed, illustrated, or blank sheets, made of paper, parchment, or other material, usually fastened together to hinge at one side. A single sheet within a book is called a leaf, and each side of a leaf is called a page. A book produced in electronic format is known as an e-book.

Books may also refer to a literature work, or a main division of such a work. In library and information science, a book is called a monograph, to distinguish it from serial periodicals such as magazines, journals or newspapers. The body of all written works including books is literature.

In novels, a book may be divided into several large sections, also called books (Book 1, Book 2, Book 3, etc).

A lover of books is usually referred to as a bibliophile, a bibliophilist, or a philobiblist, or, more informally, a bookworm.

A store where books are bought and sold is a bookstore or bookshop. Books can also be borrowed from libraries.