Molecular properties and reactions are controlled by electrons in the molecules. Electrons had been thought to be particles. Quantum mechanics showed that el- trons have properties not only as particles but also as waves. A chemical theory is required to think about the wave properties of electrons in molecules. These prop- ties are well represented by orbitals, which contain the amplitude and phase ch- acteristics of waves. This volume is a result of our attempt to establish a theory of chemistry in terms of orbitals -- A Chemical Orbital Theory. The amplitude of orbitals represents a...