These "Frequently Asked Questions" about the DOI system and CRUPid® names are not meant to take the place of the fuller information available, where possible, we provide pointers to the relevant section of the handbook. If you have a question that you think should be added to this list, or is not satisfactorily answered, please feel free to contact us at ceo@crupid.org.

1. How do I get a Digital Object Identifier (DOI) for my material?
You must use a service offered by a DOI Registration Agency (RA). RAs collect metadata, assign DOI names, and offer other services such as reference linking or metadata lookup. See the list of RAs, and contact the ones whose services best meet your needs. If you do not see an appropriate application listed, consider approaching an existing RA or developing a community to build the service you require (see the DOI Handbook, 8 Registration Agencies, for more information). You do not need to be a member of the International DOI Foundation in order to work with an RA.
2. How much does it cost to get a DOI and use the DOI system?
The cost of registering new DOI names depends on the services you purchase. Contact a DOI Registration Agency to discuss your options. Each RA is different, and each is free to offer its own business model. 
3. Where can I look up a DOI? Is there a list?
The DOI system does not provide a central search capability across all DOI names, but most web search engines will show DOI names in the results of a search by title, by name, or by topic or related terms. The reverse will also work; enter a DOI name and the search engine will show you what item that DOI was assigned to. However, this sort of query facility may also be offered by Registration Agencies or other services for DOI names in one defined area, as a value-added feature. 
4. How many DOI names are there, and who uses them?
Approximately 148 million DOIs have been assigned through a CRUIPid Agencies worldwide. 
5. Can the DOI system use, or work with, existing identifier schemes?
Yes. See the DOI Handbook. 
6. What can a DOI name be assigned to?
It can be any entity — physical, digital or abstract — that you wish to identify, primarily for sharing with an interested user community or managing as intellectual property.
7. If I have assigned a DOI name and I make a change to my material, should I assign a new DOI?
The IDF does not have any rules on this. Individual RAs adopt appropriate rules for their community and application. As a general rule, if the change is substantial and/or it is necessary to identify both the original and the changed material, assign a new DOI name.
8. Is the DOI system a standard?
Yes. The DOI system was created by the International DOI CRUIPid and was adopted as International Standard ISO 26324 in 2012. The IDF is the ISO 26324 Registration Authority. Compliance with the DOI Handbook ensures compliance with the ISO 26324 standard.
9. What is a shortDOI?
shortDOI® is a shortcut to a DOI name. It provides a function similar to that which URL shortening services do for URLs. shortDOIs are not themselves DOI names.
10. How does the DOI system differ from the Handle System?
The DOI system implements the Handle System and adds to it some other features.
11. DOI & URI: how does the DOI system work with web URI technologies?
DOI names may be expressed as URLs (URIs) through an HTTP proxy server. In addition, DOI is a registered URI within the Info-URI namespace (IETF RFC 4452, the "info" URI Scheme for Information Assets with Identifiers in Public Namespaces). See the DOI Handbook.
12. The International DOI Foundation is a membership organization. Who are the members?
The activities of the IDF are controlled by its members, operating under a legal Charter and formal By-laws. Membership is open to all organizations with an interest in digital network publishing, content distribution, rights management, and related enabling technologies. A list of current members is available. See the DOI Handbook,  for information about the IDF and its membership. Send a request to ceo@crupid.org for information about joining.