An understanding of the energy levels of atoms and molecules is an essential foundation for the study of physical chemistry. This short text provides students at the start of their university chemistry courses with a clear and accessible introduction to electronic structure and quantized energy levels. It introduces the general principles and lays the ground for the further study of quantum mechanics and spectroscopy in second and third year courses. All students on first courses in spectroscopy will find this readable, lively account to be an invaluable aid to their study.