New edition of a well-established second and third year textbook for Physics degree students, covering the physical structure and behaviour of atoms and molecules. The aim of this new edition is to provide a unified account of the subject within an undergraduate framework, taking the opportunity to make improvements based on the teaching experience of users of the first edition, and cover important new developments in the subject. Features Revised material on molecular structure and spectra. Extended material on electronic and atomic collisions. A new chapter describing applications based on the use of the maser and the laser, including laser spectroscopy, laser cooling and trapping of atoms, Bose Einstein condensation, atom lasers and atomic systems in intense laser fields. A new chapter describing other applications, including magnetic resonance, atom optics, atoms in cavities, ions in traps, atomic clocks and astrophysics. Revised appendices include new material on molecules and updated tables of physical constants. Solutions of selected problems. Contents Electrons, photons and atoms.The elements of quantum mechanics.One-electron atoms.Interaction of one-electron atoms with electomagnetic radiation.One-electron atoms: fine structure and hyperfine structure.Interaction of one-electron atoms with external electric and magnetic fields.Two-electron atoms.Many-electron atoms.Interaction of many-electron atoms with electromagnetic radiation and with static electric and magnetic fields.Molecular structure.Molecular spectra.Atomic collisions: basic concepts and potential scattering.Electron-atom collisions and atomic photoionisation.Atom-atom collisions.Masers, lasers and their interaction with atoms and molecules.Further developments and applications of atomic and molecular physics.Appendices.