XLOOP is a new SC workshop focused on the intersection of large-scale experimental science with high-performance computing. We invite submissions and participation from experimental scientists, computer scientists, practitioners, and researchers interested in this highly multidisciplinary area. Continued advances in computing power beyond the petascale create an environment in which experimental data can be computationally modeled and thus understood at a deeper level. How is experimental science improved by high-quality simulations, and how do numerical calculations drive better experiments? How can the increasing quantities of data from sensors and detectors be managed? How are are systems to support high-performance computing designed and delivered to practicing scientists? These and other questions are welcome discussion at XLOOP. The workshop will be held in conjunction with SC19: The International Conference for High Performance Computing, Networking, Storage and Analysis located in Denver, Colorado, USA, November 17–22, 2019.