Karl Östen Elfving (27 May 1874 Vaasa – 25 July 1936 Boden, Sweden) was a Finnish agricultural expert and politician.

Elfving's brother was Karl Oskar Elfving Younger (1872–1946) and sister teacher and writer Ester Ståhlberg (1870–1950) who was the second spouse of the President of the Republic of Finland K. J. Ståhlberg since 1920.

Elfving acted as a trustee, agricultural engineer, assistant to the county agronomist and as a consultant for agriculture until 1906, then until 1917 as an Inspector in the Settlement Board and as the Chief Executive of the Settlement Board in 1917–1926.

Elfving was part of the governing bodies of several agricultural organizations and foundations and participated in state committees.

Elfving's spouse since 1909 was Aini Maria née Borg (born 1930).