Johannes de Villiers Graaff (also known as Jan de Van Graaff or Jannie Graaff; 19 February 1928 – 6 January 2015) was a South African neoclassical welfare economist. He was a former chairman of Nedbank. Graaff was known for his work on optimal savings rates and contributions to the creation of the social welfare function.
Graaff graduated from the University of Cape Town and then went on to complete his PhD in economics at St John's College, Cambridge in 1950.
On 30 June 1951, he married Lillian Clare Thomson, daughter of Sir George Paget Thomson. They had six children.
He was the youngest son of Sir David Graaff, 1st Baronet. His eldest brother is Sir De Villiers Graaff, 2nd Baronet.
Graaff was one of South Africa's most active and accomplished mountaineers, pioneering mountain climbing routes in East Africa and the Himalayas.
He died on the 6 January 2015 in Kenilworth, Cape Town, aged 86.