Ivan Morton Niven (October 25, 1915 – May 9, 1999) was Canadaian-American mathematician. He was a member of the University of Oregon faculty from 1947 to his retirement in 1981. He received the University of Oregon's Johnson Award in 1981. He was a graduate of the University of British Columbia in his undergraduate studies and was awarded his doctorate from the University of Chicago. He worked mainly in number theory.

He was president of the Mathematics Association of America from 1983 to 1994. He received the MAA Distinguished Service Award in 1989.

He died in 1999 in Eugene, Oregon.

Niven numbers are named in his honor.