The ESTEC Crew Workstation Test-Bed is an experimental laboratory and reference facility for upstream engineering in support of ESA's manned space activities. It enables the assessment of concepts and technologies for crew working environments and for on-orbit operation of the manned space systems. As well as a conventional laboratory environment for stand-alone assessment of particular technologies, the Test-Bed includes a full scale mock-up of the Columbus Attached Laboratory fitted out with prototype payloads, utilities, and crew terminals; this has provided the first practical forum for bringing together the latest thinking of the Columbus development and utilisation teams. Since early 1992 the mock-up has been used for simulations of typical crew activity scenarios, oriented mainly towards payload operations. The overall objectives of the simulations were to assess new techniques in a realistic operational environment, to practice crew operations, and to explore optimum cooperation of the onboard hardware, software, and crew resources, together with the ground resources, in order to improve the practicality and cost-effectiveness of Columbus as a facility for the advancement of science.