Seidl is the surname of:
- Anton Seidl (1850–1898), Hungarian conductor
- Gabriel von Seidl (1848-1913), German architect
- Johann Gabriel Seidl (1804-1875), Austrian archaeologist, lyricist, narrator and dramatist
- Otto Seidl (born 1931), until 1998 vice-president of the German Supreme Court
- Siegfried Seidl (1911-1947), Commander of the concentration camp at Theresienstadt
- Ulrich Seidl (born 1952), director, screen writer and producer
- Florian Seidl (born 1979), vehicle designer
Seydel is the surname of:
- Christian August Seydel, founder of C. A. Seydel Söhne, a harmonica factory
- Anton Gilbert Edler von Seydel, Honorary Citizen of Vienna
- Karl Theodor Seydel, former mayor of Berlin
- Rudolf Seydel (1835-1892), German philosopher