PROJECT SUMMARY In pursuit of a diagnosis, many patients undergo countless tests and procedures in hopes of finding answers. When these fail to yield diagnoses, patients are left in a state of uncertainty, faced with the possibility of never knowing the cause of their symptoms. Finding a diagnosis and other patients affected with the same, or similar, condition can reduce or eliminate this uncertainty and end the diagnostic odyssey. In our current healthcare system, it can take years before patients with rare conditions and rare presentations of common conditions receive a diagnosis- an amount of time that many of these patients simply do not have. As the Coordinating Center for the Undiagnosed Diseases Network (UDN), Harvard Medical School will support the integrated network of 8-10 clinical sites and multiple core laboratories striving to improve the level of diagnosis and care for patients with undiagnosed conditions and facilitate research into their etiologies. We will do this by leveraging our collective expertise and experience in managing multi-site studies, trans-institutional data sharing, data curation and analysis, bioinformatics, biostatistics, and translational research. In so doing, we will accomplish five aims: (1) Enhance UDN core operational processes, (2) Develop consensus across the UDN for evaluation and diagnostic approaches, (3) Follow the UDN participant beyond the diagnostic evaluation, (4) Expand the transactional and analytical intelligence applied to UDN data, and (5) Integrate a larger set of scientific and clinical care partners into the UDN.