The DCC has assembled a group of briefing papers that together form an introduction to curation. These concise overviews are designed to help grow your basic understanding of key curation issues by providing a high-level introduction to a given topic. The persistent identification of digital resources can play a vital role in enabling their accessibility and re-usability over time. However, progress in defining the nature and functional requirements for identifier systems is hindered by a lack of shared agreement on what identifiers should actually do. To some, an identifier system is strictly a means of providing a unique name to a digital or analogue resource — either globally or locally. To others, identifier systems must also incorporate associated services such as resolution and metadata binding. Specific requirements will differ, but it is vital that institutions recognise that the application and maintenance of identifiers forms just one part of an overall digital preservation strategy. Without adequate institutional commitment and clearly defined roles and responsibilities, identifiers cannot offer any guarantees of persistence, locatability, or actionability in the long or short-term.