Adriaan van Roomen (29 September 1561 – 4 May 1615), also known as Adrianus Romanus, was a Flemish mathematician.
Van Roomen was born in Leuven, the son of Adriaan Van Roomen and Maria Van Den Daele. He became a professor, and then travelled extensively in Europe.
After studying at the Jesuit College in Cologne, Roomen studied medicine at Leuven. Roomen was professor of mathematics and medicine at Louvain from 1586 to 1592, he then went to Würzburg where again he was professor of medicine and became "Mathematician to the Chapter". He met Kepler, and discussed with François Viète two questions about equations and tangencies. He then spent some time in Italy, particularly with Clavius in Rome in 1585.
He was ordained a priest in 1604. After 1610 he tutored mathematics in Poland.
He worked in algebra, trigonometry and geometry; and on the decimal expansion of π.
His publication of 1595, Parvum theatrum urbium, contained Latin verse on the cities of Italy (possibly written by Thomas Edwards).
He solved the Problem of Apollonius using a new method that involved intersecting hyperbolas.