Original text and detailed historical commentary by Claus Kiefer. The work of Einstein, Podolsky, and Rosen (EPR) from 1935 is considered a classic of modern physics. It addresses for the first time the central property of quantum theory: entanglement. In general, systems in nature are entangled, meaning they share a common, indivisible state. This fact is responsible for all the peculiarities commonly associated with quantum theory, including the thought experiments involving Schrödinger's cat and Wigner's friend. The entanglement of quantum mechanical systems plays a central role in experiments with atoms and photons (Nobel Prize 2012 for Haroche and Wineland) and in the planned construction of quantum computers. The book presents the original EPR paper in German.