A book is a set or collection of written, printed, illustrated, or blank sheets, made of paper, parchment, or other various 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 electronic book (e-book).

Books may also refer to works of literature, 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 and sometimes other types of books (e.g. biographies), 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.