Why do molecules adopt particular shapes? What determines the physical and chemical properties of a material? This text answers these questions by introducing the ideas behind molecular and quantum mechanics, using a largely non-mathematical approach. Atomic and molecular orbitals, computational chemistry and bonding in solids are also discussed. A case study, Molecular Modelling in Drug Design , explores ways in which computer modelling, in conjunction with experimental techniques, is used to design new drugs. The accompanying CD-ROM illustrates applications of molecular and quantum mechanics, and includes many of the structures and orbitals illustrated in the text. It provides the programs necessary to view orbitals and 3D structures.