This award supports research in the study of the interaction of positrons with atoms and molecules. A number of physical processes will be investigated, including the determination of low-energy, differential elastic and inelastic scattering cross sections and the excitation of molecular vibrations. Specific attention will be paid to trying to understand the anomalously large annihilation rates observed for molecules containing more than a few atoms and the study of positron annihilation as a function of positron energy near the threshold for positronium atom formation.