Project Summary The mission of the Microscopy and Histopathology Core B is to provide HDDC members with basic and advanced microscope equipment, services and training, image processing resources, histology and histopathology support, and support for experimental design and scientific analysis that are essential for research in the digestive diseases. Core B, which is a long-standing component of the HDDC, is a successful collaboration among three independent imaging-based cores with their own financial structure that are each led by a director. The three sites are Beth Israel Deaconess Medical Center (Site A), Boston Children’s Hospital (Site B), and Brigham and Women’s Hospital (Site C). The three core sites are physically close to one another and unified by a Core Director who oversees the relationship of each satellite core with the HDDC and its membership. This infrastructure greatly benefits the HDDC membership by providing imaging equipment and expertise in locations highly populated with HDDC users while also providing options to amplify investigator-initiated research programs and enable new experimental approaches. This infrastructure also allows for the successful integration of other Harvard-based core facilities specializing in advanced instrumentation. Nine services were offered for Core B in the past 5-year grant cycle with 39 HDDC Principal Members and 13 Affiliate Members using Core B. Overall Core B recorded on average 4,200 billable service hours/year and 16,858 total billable hours over the last 4 year grant cycle (2015-2019) with 95 (primary use), 42 (secondary use), and 1 (tertiary use) original papers emerging from Core B utilization. HDDC support significantly extended grant dollars by reducing the cost of services by 25% or more for HDDC members. New innovations and equipment updates in the past grant cycle benefited, in particular, the electron microscopy and confocal microscopy services and their users. In the next grant cycle, the same nine services will be offered in Core B with 64 members indicating an interest in using Core B services. In the advanced microscopy category, one new service in high resolution 3-D electron microscopy will be available to HDDC members. Discounted services for HDDC Principal Members will continue to extend grant dollars and priority access for all HDDC members should facilitate greater productivity with cutting-edge instrumentation and expertise in the next grant cycle.