This textbook provides an accessible description of the basic concepts of atomic and molecular quantum structure, and how we probe that structure using light. The ideas described here underpin many aspects of modern science in fields such as quantum computing, astrophysics and astronomy, environmental and atmospheric chemistry, and nanotechnology, to name a few. The content of this book is appropriate for those who are new to the field, such as undergraduate students, and can also be a valuable reference for non-practitioners who are interested in the subject. There are many in-chapter...