Ismaël Boulliau (French: [buljo]; Latin: Ismaël Bullialdus; 28 September 1605 – 25 November 1694) was a 17th-century French astronomer, mathematician, and Catholic priest, who was also interested in history, theology, classical studies, and philology. He was an active member of the Republic of Letters, an intellectual community that exchanged ideas. An early defender of the ideas of Nicolaus Copernicus, Johannes Kepler and Galileo Galilei, Ismael Bullialdus has been called "the most noted astronomer of his generation". One of his books is Astronomia Philolaica (1645).
