Lysander Spooner (January 19, 1808 - May 14, 1887) was an American political philosopher, essayist, pamphlet writer, Unitarian, abolitionist, legal theorist, and entrepreneur of the 19th century. He was a strong advocate of the labor movement and severely anti-authoritarian and individualist in political views.

Spooner was born on a farm in Athol, Massachusetts, on January 19, 1808, and died on May 14, 1887, in Boston. Spooner advocated what he called Natural law - or the "Science of Justice" - wherein acts of initiatory coercion against individuals and their property were considered criminal because they were immoral while the so-called criminal acts that violated only man-made (arbitrary) legislation were not necessarily criminal.

Natural law is a philosophy asserting that certain rights are inherent by virtue of human nature endowed by nature; traditionally God or a transcendent source, and can be understood universally through human reason. As determined by nature, the law of nature is implied to be universal, existing independently of the positive law of a given political order, society or nation-state.

Historically, natural law refers to the use of reason to analyze human nature to deduce binding rules of moral behavior from nature's or God's creation of reality and mankind. The concept of natural law first appeared in ancient Greek philosophy including Aristotle, and was referred to by Roman philosopher Cicero. It was subsequently alluded to in the Bible, and was then developed in the Middle Ages by Catholic philosophers such as Albert the Great, and Thomas Aquinas. During the Age of Enlightenment, modern natural law theories were further developed, combining inspiration from the Roman law, and alongside philosophies like social contract theory. It featured greatly in the works of Alberico Gentili, Francisco Suárez, Richard Hooker, Thomas Hobbes, Hugo Grotius, Samuel von Pufendorf, Matthew Hale, John Locke, Francis Hutcheson, Jean Jacques Burlamaqui, Jean Jacques Rousseau, Emmerich de Vattel, Cesare Beccaria, and Francesco Mario Pagano. It was used to challenge the divine right of kings, and became an alternative justification for the establishment of a social contract, positive law, and government - and thus legal rights - in the form of classical republicanism. Conversely, the concept of natural rights is used by others to challenge the legitimacy of all such establishments.