Klee grew up in a musical family and was himself a violinist. After much hesitation he chose to study art, not music, and he attended the Munich Academy in 1900. There his teacher was the popular symbolist and society painter Franz von Stuck. Klee later toured Italy (1901-02), responding enthusiastically to Early Christian and Byzantine art.
Klee's early works are mostly etchings and pen-and-ink drawings. These combine satirical, grotesque, and surreal elements and reveal the influence of Francisco de Goya and James Ensor, both of whom Klee admired. Two of his best-known etchings, dating from 1903, are "Virgin in a Tree" and "Two Men Meet, Each Believing the Other to Be of Higher Rank". Such peculiar, evocative titles are characteristic of Klee, and give his works an added dimension of meaning.
After his marriage in 1906 to the pianist Lili Stumpf, Klee settled in Munich, then an important center for avant-garde art. That same year he exhibited his etchings for the first time. His friendship with the painters Wassily Kandinsky and August Macke prompted him to join Der Blaue Reiter (The Blue Rider), an expressionist group that contributed much to the development of abstract art.
A turning point in Klee's career was his visit to Tunisia with Macke and Louis Molliet in 1914. He was so overwhelmed by the intense light there that he wrote: "
Color has taken possession of me; no longer do I have to chase after it, I know that it has hold of me forever. That is the significance of this blessed moment. Color and I are one. I am a painter". He now built up compositions of colored squares that have the radiance of the mosaics he saw on his Italian sojourn.
Klee often incorporated letters and numerals into his paintings. These, part of Klee's complex language of symbols and signs, are drawn from the unconscious and used to obtain a poetic amalgam of abstraction and reality. He wrote that "Art does not reproduce the visible, it makes visible", and he pursued this goal in a wide range of media using an amazingly inventive battery of techniques. Line and color predominate with Klee, but he also produced series of works that explore mosaic and other effects.
Klee taught at the Bauhaus school after World War I, where his friend Kandinsky was also a faculty member. In Pedagogical Sketchbook (1925), one of his several important essays on art theory, Klee tried to define and analyze the primary visual elements and the ways in which they could be applied. In 1931 he began teaching at Dusseldorf Academy, but he was dismissed by the Nazis, who termed his work 'degenerate'.
In 1933, Klee went to Switzerland. There he came down with the crippling collagen disease scleroderma, which forced him to develop a simpler style and eventually killed him. The late works, characterized by heavy black lines, are often reflections on death and war.