Current literature focusing on the prosthetic socket is limited by measurement techniques and modeling assumptions, leading to a limited understanding of the forces and motions occurring between the residual limb and prosthesis and how they can be used to influence socket design and fitting. Prosthetic socket fitting and prescription would benefit from an elegant method for comparing socket designs. This dissertation focuses on the development and implementation of a 3D motion capture model and a Slip Detection Sensor to quantify rotations and translations at the prosthetic socket-residual limb interface. The 3D motion capture model defines the residual limb bone position inside the prosthetic socket which allows for measurement of the movement occurring at the prosthetic socket interface. The Slip Detection Sensor is an optoelectronic sensor embedded into the prosthetic socket wall to measure the amount of socket slip occurring between the socket wall and the residual limb skin surface. The motion capture model and Slip Detection Sensor were used to measure motion at the socket interface of transhumeral amputees during activities of daily living. Data were collected on six transhumeral amputees in the University of South Florida's (USF) motion analysis laboratory. One of the participants completed the collection procedures twice using two different suspension systems (pin locking versus no pin locking) within the same socket. An eight camera Vicon (Oxord, UK) motion capture system was used to collect kinematic data for each participant during the repetition of a series of range of motion (RoM) and activities of daily living (ADL). The RoM tasks included shoulder flexion/extension, shoulder abduction/adduction, shoulder rotation, and elbow flexion. The ADL tasks included a bilateral and unilateral lifting task at various weight increments, modified box and blocks test, folding a towel, and walk and carry a gallon jug of water. The impact of donning the prosthesis on the participant's RoM and the amount of socket movement during the ADL tasks was analyzed. The results show that the participant's shoulder RoM significantly decreased while wearing their prosthesis compared to when they were not wearing their prosthesis. The anterior-posterior tilt, medial-lateral tilt, and socket vertical translation were more directly correlated with the amount of residual limb movement than with the force acting on the prosthetic hand. Socket slip was most directly correlated with the force acting on the prosthetic hand. The results also show that the amount of translation was reduced when the pin locking suspension was used compared to when it wasn't for the individual participant who used both suspension systems within the same socket. The motion capture data were used to determine the amount of socket movement during activities of daily living while avoiding many of the limitations of other socket interface studies. The Slip Detection Sensor provided experimental data on the amount of slip occurring between the residual limb skin surface and socket wall. This method seems to be a useful tool for evaluating socket performance in terms of movement. Ultimately, socket interface movement data can be used to providing clinicians with quantitative results of a good socket fit to aid in the socket fitting and prescription process and incorporated into adjustable interfaces. Collection of data on more participants with various socket types is needed to make more general conclusions.