Irwin Edman was an American philosopher and professor of philosophy.

Isaac Asimov was an American writer and professor of biochemistry at Boston University. During his lifetime, Asimov was considered one of the "Big Three" science fiction writers, along with Robert A. Heinlein and Arthur C. Clarke. A prolific writer, he wrote or edited more than 500 books. He also wrote an estimated 90,000 letters and postcards. Best known for his hard science fiction, Asimov also wrote mysteries and fantasy, as well as much non-fiction.

Isaac Barrow was an English Christian theologian and mathematician who is generally given credit for his early role in the development of infinitesimal calculus; in particular, for proof of the fundamental theorem of calculus. His work centered on the properties of the tangent; Barrow was the first to calculate the tangents of the kappa curve. He is also notable for being the inaugural holder of the prestigious Lucasian Professorship of Mathematics, a post later held by his student, Isaac Newton.

Isaac Deutscher was a Polish Marxist writer, journalist and political activist who moved to the United Kingdom before the outbreak of World War II. He is best known as a biographer of Leon Trotsky and Joseph Stalin and as a commentator on Soviet affairs. His three-volume biography of Trotsky was highly influential among the British New Left in the 1960s and 1970s.

Isaac Husik was a Jewish historian, translator, and student of philosophy, one of the first three individuals to serve as official faculty at Gratz College in Philadelphia.

Sir Isaac Newton was an English mathematician, physicist, astronomer, alchemist, theologian, and author who was described in his time as a natural philosopher. He was a key figure in the Scientific Revolution and the Enlightenment that followed. His pioneering book Philosophiæ Naturalis Principia Mathematica, first published in 1687, consolidated many previous results and established classical mechanics. Newton also made seminal contributions to optics, and shares credit with German mathematician Gottfried Wilhelm Leibniz for developing infinitesimal calculus.

Isaac Rosenberg was an English poet and artist. His Poems from the Trenches are recognized as some of the most outstanding poetry written during the First World War.

Isaac Taylor was an English philosophical and historical writer, artist, and inventor.

Isaac Watts was an English Congregational minister, hymn writer, theologian, and logician. He was a prolific and popular hymn writer and is credited with some 750 hymns. His works include "When I Survey the Wondrous Cross", "Joy to the World", and "Our God, Our Help in Ages Past". He is recognised as the "Godfather of English Hymnody"; many of his hymns remain in use today and have been translated into numerous languages.

Isaac Weld JP FGSD MRIA (1774–1856) was an Anglo-Irish topographical writer, explorer, and artist. He travelled extensively in North America was a member of the Royal Dublin Society.