The Two Phase Flow (TPF) Experiment is an integrated two-phase thermal control system designed to address capillary pumped loop component and system performance issues. The Two Phase Flow Experiment was flown aboard the Space Shuttle Discovery (STS-85) from August 7 - 19, 1997 as part of the Technology Applications and Science-01 (TAS-01) mission. The experiment was contained in a Hitchhiker canister and consisted of a capillary pumped loop (CPL), electronics, and associated instrumentation and wiring. The CPL contained four capillary evaporators (two large diameter and two small diameter), two parallel condensers, a two-phase temperature controlled reservoir, liquid and vapor tubing, individual capillary isolators, and a capillary vapor flow valve. The system working fluid was anhydrous ammonia.The system was operated for a total of 176 hours during the mission with 61 test cycles performed. Tests performed included start-ups, low power tests, high power tests, individual heat pipe tests, long term operation, and pressure priming. Tests were performed with a single evaporator operating and with all four evaporators operating simultaneously. This paper will describe the system design in detail, and will discuss flight test results.