Leif Selim Segerstam[1] (/ˈleɪf/ LAYF, 2 March 1944 – 9 October 2024) was a Finnish conductor, composer, violinist, violist, and pianist, especially known for writing over 300 symphonies, along with other works.

He is widely known through his recordings, including the complete symphonies of Blomdahl, Brahms, Mahler, Nielsen, and Sibelius, as well as many works by contemporary composers.

[6] Segerstam studied at the Sibelius Academy in Helsinki,[1][9] piano with Jaakko Somero, violin with Leena Siukonen-Penttilä, composition with Einar Englund and Joonas Kokkonen, and conducting with Jussi Jalas.

[10] He studied further at the Juilliard School in New York City,[9] violin with Louis Persinger, composition with Hall Overton and Vincent Persichetti, and conducting with Jean Morel,[5] and received his postgraduate diploma in 1965.

[10][13] He conducted as a guest at the Metropolitan Opera in New York City, La Scala in Milan and the Royal Opera House in London, with a repertoire including Verdi's Aida and Don Carlo, R. Strauss' Salome and Elektra and Wagner's Tannhäuser and Der fliegende Holländer.

[9][14] His students include Rune Bergmann,[16] Susanna Mälkki,[15] Mikk Murdvee, Sasha Mäkilä and Markku Laakso.

[14] His 37th symphony, for example, at its premiere featured Segerstam at the piano, leading the orchestra "in a relatively free form".

[27] This composition approach proved to be a quick way of writing large blocks of sound (the temporal order of events being left to the performer) and permitted an exceptionally prolific output.

[6][26] He composed 30 string quartets and numerous concertos, for violin, viola, cello and piano.

[14][32][33][2] Segerstam is widely known through his recordings, which include the complete symphonies of Blomdahl, Brahms, Mahler, Nielsen, and Sibelius, as well as many works by contemporary composers, such as the Americans John Corigliano and Christopher Rouse, the Finnish Einojuhani Rautavaara, Swedish Allan Pettersson, and the Russian Alfred Schnittke.