ENSDF contains evaluated nuclear structure and decay data in a standard format. An international network of evaluators contributes to the database, which is maintained by the National Nuclear Data Center at Brookhaven National Laboratory. Information in the database is regularly updated to reflect revised evaluation results. Most of the recently completed evaluations are published in Nuclear Data Sheets, a monthly journal published by Academic Press, a division of Elsevier Science.

For each nuclide, all known experimental data used to deduce nuclear structure information are included. Each type of experiment is presented as a separate dataset. In addition, there is a dataset of "adopted" level and gamma-ray transition properties, which represent the evaluator's determination of the best values for these properties, based on all available experimental data.

As of the most recent update on Unknown, the ENSDF database contains 19779 datasets for 3438 nuclides.