Paul Klee began teaching at the Staatliches Bauhaus in Weimar on 10 January 1921, where he mixed with a group of leading contemporary artists. Initially he travelled to Weimar every fortnight for periods of 14 days until he moved there definitively in September 1921.

His teaching modules consisted of a theoretical lecture on design theory in the morning and practical courses in the afternoon. Artistic training at the Bauhaus around that time focused on inculcating a precise understanding of form and the laws by which it is governed. In mid-April Klee took over the bookbinding workshop as form master. In 1922–1923 he was head of the Atelier für Glasmalerei (glass painting workshop).

While teaching at the Bauhaus Klee concentrated on deepening and broadening his previous experience, expounding the methodology, and establishing the theory of his artistic principles. Virtually all the documents on his lectures have been preserved, including Klee’s Beiträge zur bildnerischen Formlehre (Contributions to the theory of form) from his 1921-1922 Bauhaus course. Besides teaching, Klee also worked intensively on his painting work.

In 1919 Klee developed a personal tracing method, which enabled him to copy pencil, ink and Indian ink drawings and work them into multi-coloured sheets (aquarelled oil drawings). During his first few years at Weimar (1921–1923) he used the possibilities of this new tracing method a great deal. In fact the possibilities offered by the new technique are particularly evident in paintings such as Fesselung, 1920, 168 (Fettering ) and Lied des Spottvogels, 1924, 66 (Song of the mockingbird).

At the same time Klee perfected his aquarelling technique. By systematically superimposing layers of paint, he achieved the finest graduations of colour and tone.

At the Bauhaus Klee closely studied the elementary square-picture structures originally devised by Piet Mondrain and Theo van Doesburg. For Klee the strict reduction of pictorial means was but one possibility to be pursued, and he never elevated it to a rigid, universal principle.

The repercussions of the economic crisis and in particular of soaring inflation reduced to virtually nothing Klee’s earnings from his steadily increasing sales. In 1921 Wilhelm Hausenstein published his monograph entitled Kairuan oder eine Geschichte vom Maler Klee und von der Kunst dieses Zeitalters (Kairuan or a History of the Artist Klee and the Art of this Age). The book had a considerable impact on the understanding of Klee and his work.

In summer 1922 Wassily Kandinsky was appointed to the Bauhaus. In summer 1923 Klee’s essay Wege des Naturstudiums (Ways of Studying Nature) was published in the catalogue for the Erste Bauhaus Ausstellung (First Bauhaus Exhibition) in Weimar. On the occasion of the exhibition Klee designed two invitation postcards that served to illustrate the polarity of the Bauhaus’s programme: its stricter, “loftier” aspect and its more playful, more “light-hearted” aspect.

At his exhibition at the Kunstverein in Jena on 26 January 1924 Klee held his famous lecture "Über moderne Kunst" (On Modern Art), which was published posthumously. In January and February of that year the Société Anonyme in New York showed the first individual exhibition of works by Paul Klee in the US. In spring 1924 the German art collector and dealer Emmy (Galka) Scheyer founded the group The Blue Four (Die Blauen Vier), comprising Lyonel Feininger, Alexej Jawlensky, Wassily Kandinsky and Paul Klee, its aim being to make the work of these artists better known in the US.

From 1923 the Bauhaus increasingly came under political pressure from right-wing circles, culminating on 26 December in the closure of the Bauhaus in Weimar.