Johann Heinrich Alsted (March 1588 – November 9, 1638), "the true parent of all the Encyclopædias", was a German-born Transylvanian Saxon Calvinist minister and academic, known for his varied interests: in Ramism and Lullism, pedagogy and encyclopedias, theology and millenarianism. His contemporaries noted that an anagram of Alstedius was sedulitas, meaning "hard work" in Latin.

Alsted was born in Mittenaar. He was educated at Herborn Academy in the state of Hesse, studying under Johannes Piscator. From 1606 he was at the University of Marburg, taught by Rudolf Goclenius, Gregorius Schönfeld and Raphaël Egli. The following year he went to Basel, where his teachers were Leonhardt Zubler for mathematics, Amandus Polanus von Polansdorf for theology, and Johann Buxtorf. From about 1608 he returned to the Herborn Academy to teach as professor of philosophy and theology.

Alsted was later in exile from the Thirty Years' War in Transylvania, where he remained for the rest of his life. In 1629 he left war-torn Germany for Weißenburg (now Alba Iulia in Romania) to found a Calvinist Academy: the context was that the Transylvanian royal family had just returned from Unitarianism to Calvinism, and Alsted and Johannes Bisterfeld were German professors brought in to improve standards. Among the students there was János Apáczai Csere.

Alsted died in Alba Iulia in 1638.

Alsted has been called 'one of the most important encyclopedists of all time'. He was a prolific writer, and his Encyclopaedia (1630) long had a high reputation. It was preceded by shorter works, including the 1608 Encyclopaedia cursus philosophici. His major encyclopedia of 1630, the Encyclopaedia, Septem Tomis Distincta, was divided into 35 books, and had 48 synoptical tables as well as an index. Alsted described it as "a methodical systemization of all things which ought to be learned by men in this life. In short, it is the totality of knowledge." In its time it was praised by Bernard Lamy and Cotton Mather, and it informed the work of Alsted's student John Amos Comenius. An unfinished encyclopedic project by Gottfried Wilhelm Leibniz began as a plan to expand and modernize it, and the famous diarist Samuel Pepys purchased a copy in 1660—thirty years after its initial publication. Although Jacob Thomasius criticised it for plagiarism for verbatim copying without acknowledgment, Augustus De Morgan later called it "the true parent of all the Encyclopædias, or collections of treatises, or works in which that character predominates".

The Cambridge History of Renaissance Philosophy, p. 632, in the context of Calvinist metaphysics, states

"In the works of authors like Clemens Timpler of Heidelberg and Steinfurt, Bartolomaeus Keckermann of Heidelberg and Danzig, and Johann Heinrich Alsted of Herborn there appeared a new, unified vision of the encyclopaedia of the scientific disciplines in which ontology had the role of assigning to each of the particular sciences its proper domain."

In his The New England Mind, Perry Miller writes about the Encyclopaedia: