A Quad-Redundant Thermal Switch (QRTS) for the James Webb Space Telescope has been successfully designed, fabricated, and tested at the Space Dynamics Laboratory (SDL). A flight-like prototype successfully passed thermal and structural qualification tests in a representative space environment and achieved Technology Readiness Level 6. The QRTS serves as a high thermal conductance, high reliability thermal connect/disconnect between heat sources and sinks. The switch design is passively closed over the entire operational range of 32–300 K. The construction is an all metallic core packaged in a cross-strapped quad-redundant configuration. Actuation of the switch is based on differential thermal expansion and is opened by applying heat to the mechanism. Key qualification tests included: robust characterization of thermal closed and open performance from 32 to 313 K; and a full suite of vibration testing (sine, random, and sine burst). This paper presents an overview of the QRTS functionality, thermal and str...