The Leviathan is a book written by Thomas Hobbes titled after sea monster referred to in the Bible. It's much longer name is The Matter, Forme and Power of a Common Wealth Ecclesiasticall and Civil. The book mainly talks about what a legitimate government is and the structure of society. It is regarded as one of the very first books that touched the concept of social contract theory. It is because of this that it has become one of the most influential political books.

The book can be divided into four parts: of Man, of Common-wealth, of a Christian Common-wealth and of the kingdom of darkness.

The first part of the book discusses the very core of society – the man and the way man makes up definitions in relation to man's biases. Some of the concepts given a new set of definitions are good, evil, appetite, hope, imagination, memory, among others. It is also in this part where Hobbes introduces one of the famous lines in the book which is “the life of man, solitary, poor, nasty, brutish, and short.” This short line tries to define the state of existence of men which is always in conflict against other men. Such conflicts were expounded as competition, diffidence and joy. According to the book, competition makes men invade for profit, while diffidence for safety and glory for reputation. In fact, every man has the right to everything. Yet, men usually waive this right in order to attain order. Thus, certain covenants or contracts are made.

The second part, the common-wealth, explains that men, whose nature is to dominate and to be free chooses to restrain themselves in order to keep themselves from the ill effects of war. Thus, the commonwealth is put up. The instituted commonwealth follows twelve principles. Among these twelve principles are: the form of government could not be lawfully changed by the subjects; the sovereign cannot breach the covenant and its subjects could not ask to be freed from the covenant made; the existence of the sovereignty has been consented by the majority and is abided by the minority; and, many more. It further discusses monarchy, aristocracy and democracy, the three forms of commonwealth. Lastly, it also explains the concept of succession, religion and taxation in relevance to the commonwealth.