Digital Object Identifiers, or DOIs, guarantee the persistent identification and citation of electronic publications and research data – and they are steadily taking on an increasingly important role. In mid-August 2013, the non-profit organization DataCite assigned its two-millionth DOI. As a DataCite member, the German National Library of Medicine (ZB MED) in Cologne and Bonn operates as a registration agency for DOIs in the fields of medicine, health, nutrition, the environment and agricultural science. This service is free for academic institutions located in Germany.

Increasing numbers of researchers are choosing to publish their research findings and data exclusively online. This development has made it necessary to create permanent identifiers for publications and research data to ensure they can be readily cited and easily found. DOIs provide a permanent and unique path to electronic resources, making them a vital part of the citation process. Even if the location of the data changes, all that is required is to update the URL in the metadata associated with the archived object. The DOI name remains unchanged and is permanently linked to the object. The assignment of a DOI makes research data citable in a similar way to publications. It offers a useful means of facilitating and promoting data sharing.

For researchers from the fields of medicine, health, nutrition, and environmental and agricultural sciences, the ZB MED is a useful point of contact for DOI-related issues. In collaboration with the German National Library of Science and Technology (TIB) in Hannover, the ZB MED operates as a DOI registration agency in Germany. The library is a member of DataCite e.V., an international non-profit association that provides services and know-how regarding the citation and referencing of research data. "We're hoping that by offering this service we will encourage more researchers to publish their findings and data on the Internet," says Ulrich Korwitz, Director of the ZB MED.

For more information on assigning DOIs, please contact Gabriele Wollnik-Korn, phone: +49 (0) 228 73 3403, e-mail: doi-service@zbmed.de or visit www.zbmed.de/publikationsservice/doi-service.html.