Kinematic couplings are routinely used in instruments and optical systems to precisely (repeat ably) position one object with respect to another. Typical instruments and optical systems contain few dynamic elements that induce vibrations, and they frequently include passive or active systems to isolate transmission of ground vibrations. As a result, kinematic couplings can be designed without considering dynamic performance. In fact, kinematically coupled bodies are generally assumed to be rigid. More recently, kinematic couplings are finding a variety of applications in manufacturing processes and machinery where improved precision can improve process repeatability. In manufacturing applications, kinematically coupled bodies are subjected to dynamic excitation from moving machine elements, process dynamics, and noise transmitted from the factory floor. In these circumstances, the rigid body assumption is no longer applicable, and significant errors may arise due to vibrations within the kinematically coupled structure. In this paper, the dynamic nature of kinematically coupled structures are investigated for a fundamental configuration - flexible, rectangular plates attached to rigid bases via three-groove kinematic couplings-using experimental modal analysis. Interaction of rigid base plate with the main plate is investigated.