The use of piezoelectric ceramic materials for structural actuation is a fairly well developed practice that has found use in a wide variety of applications. However, actuators with piezoceramic fibers and interdigitated electrodes have risen to the forefront of the intelligent structures community due to their increased actuation capability. However, their fiber-reinforced construction causes them to exhibit anisotropic piezomechanical properties, and the required larger driving voltages make the inherent piezoelectric nonlinearities more prevalent. In order to effectively utilize their increased performance, the more complicated behavior of these actuators must be sufficiently characterized. The current work is intended to provide a detailed nonlinear characterization of the mechanical and piezoelectric behavior of the Macro Fiber Composite actuator, which was developed at the NASA Langley Research Center. The mechanical behavior of this planar actuation device, which is both flexible and robust, is investigated by first developing a classical lamination model to predict its short-circuit linear-elastic properties, which are then verified experimentally. The sensitivity of this model to variations in constituent material properties is also studied. Phenomenological models are then used to represent the measured nonlinear short-circuit stress-strain response to various in-plane mechanical loads. Piezoelectric characterization begins with a nonlinear actuation model whose material parameters are determined experimentally for monotonically increasing electric fields. Next, the response of the actuator to a sinusoidal electric field input is measured under various constant mechanical loads and field amplitudes. From this procedure, the common linear piezoelectric strain coefficients are presented as a function of electric field amplitude and applied stress. In addition, a Preisach model is developed that uses the collected data sets to predict the hysteretic piezoelectric behavior of the MFC. Lastly, other related topics, such as manufacturing, cure kinetics modeling and linear thermoelasticity of the Macro Fiber Composite, are covered in the appendices. / Ph. D.