Jorma J. Rissanen (born October 20, 1932 in Pielisjärvi (now in Lieksa), Finland) is an information theorist, known for inventing the arithmetic coding technique of lossless data compression, and the minimum description length principle.
An IBM researcher since 1960, Rissanen received his Ph.D. from the Helsinki University of Technology in 1965. Retired from IBM, he is now professor emeritus of Tampere University of Technology, and a fellow of Helsinki Institute for Information Technology. He was awarded the IEEE Richard W. Hamming Medal in 1993, a Golden Jubilee Award for Technological Innovation from the IEEE Information Theory Society in 1998, the Kolmogorov Medal in 2006, and the IEEE Claude E. Shannon Award in 2009. A Festschrift collection was published to honor his 75th birthday.