Johan Svendsen is one of the most influential Scandinavian composers of the nineteenth century. He contributed in particular to the orchestral repertoire in Scandinavia and he was a celebrated conductor throughout Europe. This thesis presents the first thorough examination of all surviving sketches and compositional exercises from Svendsen’s hand. The study has two main objectives: first a philological mapping of the physical sources and, second, a discussion of the act of writing music, and how this act influenced the composer’s imagination, musical style and aesthetics. It is also discussed whether Svendsen’s relatively limited repertoire of sketching methods impacted on his compositional drought from his fourties. The central sources, found in 2007, are six notebooks containing both exercises written in Leipzig in 1864–65 and sketches written mainly in Christiania in the 1870s and 80s. Otherwise, sketches survive on loose leaves, in almanacs and autograph scores for a number of completed works. This material emerged over Svendsen’s lifetime, but it presents itself as a landscape of fixed objects today. What the sketches ‘express’ is interpreted based upon their visual appearance, physical position, musical content, relationship to other sources, and knowledge of Svendsen’s life and oeuvre. The genesis of Svendsen’s mature works is elucidated through his sketching habits, compositional exercises and juvenilia. Works have emerged from broad perspectives, from a host of alternatives to a set of ‘aesthetically harmonised solutions’ represented in the fixed objects of published scores. Musical ideas have wandered from one work to another, even over the course of decades before they found their ‘home’ in a completed work, and some ideas are ‘still circling’ with their immanent potentialities, such as in the drafts for a lost or unfinished symphony. The ‘openness’ that sketches present in relation to completed scores distorts our understanding of the intention behind them. This study of the fixed documents proposes a dialectical understanding of the open and the hidden, of possibilities and restrictions, as panoramic constraints.