In this paper, an approximate analytical model is developed for the excitation of a thin beam by a single piezoelectric actuator bonded to the surface of the beam. The premise of this work is to investigate the excitation of beams by piezoelectric actuators on a more fundamental level than present work, and then use the asymmetric model to predict a wave response, rather than a modal response, on more complicated structure/actuator systems. It is determined that the single surface mounted piezoelectric actuator simultaneously excites both flexural and extensional motion in beams whose relative amplitudes are functions of beam/actuator geometry and properties. The model is then applied to the excitation of an infinite beam by two colocated arbitrarily driven actuators. It is shown that this configuration can produce any desired combination of flexural and extensional waves in beams by varying the degree of asymmetry between the actuators.