This edited, multi-author book gathers selected, peer-reviewed contributions based on papers presented at the 23rd International Workshop on Quantum Systems in Chemistry, Physics, and Biology (QSCP-XXIII), held in Mopani Camp, The Kruger National Park, South Africa, in September 2018. The content is primarily intended for scholars, researchers, and graduate students working at universities and scientific institutes who are interested in the structure, properties, dynamics, and spectroscopy of atoms, molecules, biological systems, and condensed matter.