Biomechanics is the study of the structure and function of biological systems by means of mechanics. Functional mandibular movement is defined as all the normal, proper, or characteristic of three-dimensional movements of the mandible during speech, mastication, swallowing, and other associated movements. Most functional movement occurs during mastication and speech. A removable partial denture (RPD) is not rigidly attached to the teeth, and therefore there is a potential for movement of the denture when these functional movements create forces on the teeth and denture. The practitioner should begin with the understanding of how these three-dimensional functional forces (mechanics) act on the biological environment (abutment teeth, residual ridges, and alveolar mucosa). During treatment planning of the RPD, the clinician must consider the biomechanics of the RPD as well as the patient’s comfort, esthetics, and prognosis of the abutments to withstand the forces.