The National Sleep Research Resource (NSRR), funded by the NHLBI, offers free web access at sleepdata.org to “big data” collections of de-identified physiological signals and data elements collected in well-characterized research cohorts and clinical trials. Users can query and search across thousands of data elements, identify those of most relevance and explore their statistical distributions. Polysomnography (PSG) recordings are available in downloadable European Data Format (EDF). Users can also download standard annotations and derived summary measures. The first data sets available include the over 8,000 studies from Exams 1 and 2 from the Sleep Heart Health Study (SHHS), with new data releases scheduled every quarter. The NSRR also provides open-source software for viewing and analyzing these data. Access is intended to spur hypothesis generation and testing, cross-cohort analysis of risk factors and outcomes, development of new signal processing tools, and to enhance training in clinical analysis, signal processing, epidemiological analysis, and understanding of brain function in health and disease.