Since the 1880s, electrical energies started circulating in European theaters, generated from fossil fuels in urban power plants. A mysterious force, which was still traded as romantic life force by some and for others had already come to stand in for progress, entered performance venues. Engineering knowledge, control techniques and supply chains changed fundamentally how theater was made and thought of. The mechanical image machine from Renaissance and Baroque times was transformed into a thermodynamic engine. Modern theater turned out to be electrified theater. – Retracing what happened backstage before the Avantgarde took to the front stage, this book proposes to write the genealogy of theaters modernity as a cultural history of theater technology.