This volume contains peer-reviewed contributions based on talks presented at the 26th International Workshop on Quantum Systems in Chemistry, Physics, and Biology held in Jaipur, India, in October 2023. It provides an in-depth discussion of methodological approaches that are relevant across various length scales, elucidating their applications in diverse chemical and biological systems, such as catalysis and materials. Authored by experts in their respective fields, each chapter showcases recent developments and offers insights into the latest research trends. This book is aimed at advanced graduate students, academics, and researchers, both in university and corporation laboratories, interested in state-of-the-art and novel trends in quantum chemistry, physics, and biology, and their applications.