Ernst Leonard Lindelöf (Swedish pronunciation: [ˈlɪ̂nːdɛˌløːv]; 7 March 1870 – 4 June 1946) was a Finnish mathematician, who made contributions in real analysis, complex analysis and topology.

[1] He was secretary of the Finnish Society of Science and Letters (societas scientiarum Fennica) in its centenary year, 1938.

[2] Lindelöf studied at the University of Helsinki, where he completed his PhD in 1893, became a docent in 1895 and professor of Mathematics in 1903.

In addition to working in a number of different mathematical domains including complex analysis, conformal mappings, topology, ordinary differential equations and the gamma function, Lindelöf promoted the study of the history of Finnish mathematics.

He was the PhD supervisor for Lars Ahlfors at the University of Helsinki.