This book invites readers to explore the frontiers of atomic, molecular, and optical physics — and what lies beyond. Atomic and molecular physics is relevant to everything around us, because everything in our immediate environment is made up of atoms and molecules. That said, there are a multitude of fascinating things in the world that cannot be thought of as merely a collection of atoms and molecules. How is it that, when matter grows from a single atom or molecule into a larger and larger system, a new reality emerges with all its specific features and properties? To what extent are the properties of larger systems determined by the properties of individual atoms and molecules, rather than by the properties of the whole system as it grows? At what scales do new properties appear in the system, and how do they influence other properties in the system? This book does not provide definitive answers to these questions, but rather points the way to their resolution by presenting concrete, solvable case studies from various fields that can provide some elucidation.With contributions from leading scientists, the book covers a wide range of topics — from multiscale computational modelling, nanoscience, and plasmonic chemistry to radiation damage in biomolecular systems and the foundations of astrochemistry. Many of the research areas addressed are closely related to cutting-edge technological and medical applications, such as radiotherapy and 3D nanoprinting. Ideal for researchers and advanced students across the physical and life sciences, the volume offers a rich exploration of how physics intersects with emerging technologies and global scientific challenges.