Carl Agardh Westerlund (12 January 1831 in Berga, near Kalmar – 28 February 1908 in Ronneby) was a Swedish malacologist.
Westerlund studied at Lund University where he received his bachelor's degree in 1860 and became a Ph.D. in 1862. He worked as a temporary teacher in Malmö in 1858–1859 and in Landskrona 1860–1862, and was a teacher at the high school in Ronneby from 1862 to 1893.
Westerlund contributed much to the knowledge of the land and freshwater molluscs of the palearctic region, despite working under unfavourable conditions. His largest work was Fauna der in der paläarctischen Region... lebenden Binnenconchylien in 9 volumes published 1884–1890. He also contributed papers in ornithology and botany.