Leviathan or The Matter, Forme and Power of a Common Wealth Ecclesiasticall and Civil — commonly called simply Leviathan — is a book written by Thomas Hobbes (1588–1679) and published in 1651. Its name derives from the biblical Leviathan. The work concerns the structure of society and legitimate government, and is regarded as one of the earliest and most influential examples of social contract theory. The publisher was Andrew Crooke, partner in Andrew Crooke and William Cooke. Leviathan ranks high as a classical western work on statecraft comparable to Machiavelli's The Prince and is one of a number of related works incident upon the crisis of the English state framework of the time.

In Leviathan, which was written during the English Civil War (1642–1651), Hobbes argues for a social contract and rule by an absolute sovereign. He wrote that chaos or civil war – situations identified with a state of nature and the famous motto Bellum omnium contra omnes ("the war of all against all") – could only be averted by strong central government.

Leviathan (/lɨˈvaɪ.əθən/; Hebrew: לִוְיָתָן, Modern Livyatan Tiberian Liwyāṯān ; "twisted, coiled"), is a sea monster referred to in the Bible. In Demonology, the Leviathan is one of the seven princes of Hell and its gatekeeper (see Hellmouth). The word has become synonymous with any large sea monster or creature. In literature (e.g., Herman Melville's Moby-Dick) it refers to great whales, and in Modern Hebrew, it means simply "whale." It is described extensively in Job 41.

The Leviathan is mentioned six times in the Hebrew Bible, with Job 41:1-41:34 being dedicated to describing him in detail:

In Psalm 74 Yahweh is said to "break the heads of Leviathan in pieces" before giving his flesh to the people of the wilderness; in Psalm 104 Yahweh is praised for having made all things, including Leviathan; and in Isaiah 27:1 he is called the "wriggling serpent" who will be killed at the end of time.

Sea serpents feature prominently in the mythology of the Ancient Near East, attested as early as the 3rd millennium BCE in Sumerian iconography depicting the myth of the god Ninurta overcoming the seven-headed serpent. Examples of the storm god vs. sea serpent trope in the Ancient Near East can be seen with Baʿal vs. Yam (Canaanite), Marduk vs. Tiamat (Babylonian), and Atum vs. Nehebkau (Egyptian) among others, with attestations as early as the 2nd millennium as seen on Syrian seals.

A book is a set of written, printed, illustrated, or blank sheets, made of ink, paper, parchment, or other materials, 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 (for example, biographies), a book may be divided into several large sections, also called books (Book 1, Book 2, Book 3, and so on). A lover of books is usually referred to as a bibliophile 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. In 2010, Google estimated that since the invention of printing, approximately 130,000,000 unique titles had been published.