This dissertation examines the role of German culture – theatre, music, opera, politics, and philosophy – as a catalyst to the modernist transformations of London theatre between 1890 and 1918. It explores the ways British theatre engaged German culture, whether by emulation, adaptation, or resistance, and focuses on four major figures in the Edwardian Theatre: J. T. Grein, William Archer, Bernard Shaw, and Harley Granville Barker. Impresario J. T. Grein (1862-1935) established German theatre companies in London to introduce British theatre to the works of great German writers, actors, and directors. Scottish critic William Archer (1856-1924) used Germany as a model for his campaign to translate and produce the plays of Henrik Ibsen in London. He also advocated the formation of England’s National Theatre, using German examples of state-funded repertory theatres. Bernard Shaw (1856-1950) introduced English audiences to Richard Wagner’s operas, ideas, and productions. Shaw’s plays also enjoyed a rich production history in Germany through his working relationship with his translator, Siegfried Trebitsch. Director Harley Granville Barker (1877-1946) closely followed the careers of German directors Max Behrend and Max Reinhardt. In 1912 and 1914, Barker produced three of Shakespeare’s plays, The Winter’s Tale, Twelfth Night, and A Midsummer Night’s Dream, in which audiences and critics quickly noticed German influences. As each chapter explores these figures, it will specify and evaluate how German theatre influenced them, and whether they emulated, adapted, or resisted it. The final chapter returns to each of these figures in the context of World War I. During the four years of the war, 1914 to 1918, their relationship to German culture changed radically. Some, like Archer, turned against German culture and wrote pamphlets for the Secret War Propaganda Bureau. Shaw, meanwhile, wrote articles criticizing British leadership during the war. The war transformed the British theatre’s relationship with German culture, although Germany still affected the British theatre as it moved forward – sometimes in cautious steps, sometimes in violent leaps – towards the modern world.