New interferometers as the VLTI, the Keck-I and CHARA along with their sophisticated instrumentation have provided new levels of accuracy, spectral resolution and access to various spectral bands from the optical to the thermal infrared. Investigations are now enabled on a wealth of astrophysical sources with unprecedented levels of angular resolution and sensitivity, producing a considerable body of new, exciting scientific results. Celebrating the completion of the first phase of the VLTI development, the organisors of the ESO workshop "The Power of Optical/IR Interferometry", held in April 2005, saw an opportunity to invite the community to come together to review and discuss not just interferometers, but science with interferometers and its impact on astronomy as a whole. The workshop was also intended to showcase ideas and concepts for the future of interferometry, and in particular for the second generation of VLTI instrumentation. This volume contains the proceedings of this workshop and serves as reference for astronomers working with optical and infrared interferometry.