Ernst Toller (1893-1939) wrote a substantial body of poetry which has received negligible critical attention. This thesis argues that the poetic styles he adopted enabled him not only to examine past experiences but also to evolve strategies for the challenges he faced. His early poetry (1908-1915) shows his attempts to come to terms with love and his enthusiasm to participate in the First World War. The poetry provided him with emotional models which were then revised in the light of experience. The early Expressionist poetry (1915-1919) documents his disillusionment with the war and furnishes insights into his growing political awareness. Toller then adopted the sonnet form (1919-1921), principally in order to express the vicissitudes of prison experience in a controlled manner, and this contributed to his adjustment to incarceration. Das Schwalbenbuch (1922-1924) combines this formal control with a growing sensitivity to the potential of Expressionist verse and delivers insights into his metaphysical thinking. Vormorgan (1924) summarises his experience of war, revolution and imprisonment, in verse of considerable richness and suggestivity, indicating the positive values he intended to apply to his life on release. After its publication, Toller practically ceased to write poetry except for a very few isolated examples, one of which ('Am Fluss, an unpublished poem) points to the possibility of a sixth and masterful poetic phase of which, apart from this one poem, there is no record. This study puts forward explanations for the apparent cessation of his poetry writing after 1924, arguing that his lyrical tendencies nonetheless found expression in his writing in other genres. The thesis provides an index of Toller's entire poetic production and a collection of the unpublished poems and those no longer easily accessible.