Johannes Althusius (c. 1563 – August 12, 1638) was a German jurist and Calvinist political philosopher and father of modern federalism.
He is best known for his 1603 work, "Politica Methodice Digesta, Atque Exemplis Sacris et Profanis Illustrata". revised editions were published in 1610 and 1614. The ideas expressed therein relate to the early development of federalism in the 16th and 17th centuries and the construction of subsidiarity.
Althusius was born about 1563, to a family of modest means in Diedenshausen, County Sayn-Wittgenstein (Siegen-Wittgenstein), a Calvinist County in what is now the state of North Rhine Westphalia but was then the seat of an independent Grafschaft or County. Under the patronage of a local count, he attended the Gymnasium Philippinum in Marburg from 1577 and began his studies in 1581, concentrating in law, philosophy, and logic. He first studied Aristotle in Cologne, then studied law under Denis Godefroy at Geneva. In 1586, Althusius received his doctorate in civil and canon law from the University of Basel. While studying at Basel, Althusius lived with Johannes Grynaeus for a period of time, with whom he studied theology.
In 1586, after completing his studies, Althusius became the first professor of law at the Protestant-Calvinist Herborn Academy of Nassau County. From 1592 to 1596, he taught at the Calvinist Academy in Burgsteinfurt/Westphalia, and was afterward appointed president of the Nassau College in Siegen (removed in this town from 1594 to 1600) in 1599/1600 and in Herborn in 1602, also beginning his political career by serving as a member of the Nassau (Germany) county council. For the next several years, he became involved in various colleges throughout the area, variously serving as their president and lecturing on law and philosophy, and in 1603, he was elected to be a municipal trustee of the city of Emden, in East Frisia, where he ultimately made his fame. He became a city Syndic in 1604, which placed him at the helm of Emden's governance until his death.