Andreas Speiser is well known for his work in mathematics and philosophy. In mathematics, his main areas of interest were number theory and group theory. His book Die Theorie der Gruppen von endlicher Ordnung was published in 1923 (5th ed. 1980) as volume 5 of Springer's Grundlagen series. From 1928 to 1965 Speiser was “General Redactor” of the Euler edition, 37 volumes of which appeared in this period, among them 11 volumes that were edited by Speiser himself. As far as philosophy is concerned, Speiser published a commentary on Plato’s Parmenides (Ein Parmenideskommentar, 1937) and an account on his involvement with the philosophy of Fichte and Hegel (Elemente der Philosophie und der Mathematik, 1952). Speiser was an intellectual of the old school in the best sense of the word, his interests and his education spread over wide areas, from mathematics and philosophy to music, architecture, poetry and arts. With his article, it is the authors’ intention to explain Speiser’s work to a broader audience.