Purpose Limitation

An organisation must decide and state why it needs the data before collecting it. If it later wants a new use, it must either show the new use is compatible with the original or go back to the person, often for fresh consent. Compatibility is judged by how close the uses are, what people would reasonably expect, the nature of the data and the effect on them. Further use for archiving, statistics or research is generally treated as compatible with safeguards. The principle stops what is sometimes called function creep, where data gathered for one task drifts into others. It works with minimisation and transparency, since a vague purpose such as improving services does little to limit anything. Privacy teams check new projects against recorded purposes. A person agrees to one use, not to whatever else the organisation later thinks of.

A supermarket collects phone numbers of loyalty-card members to send offers and receipt alerts. Its insurance arm later asks for the list to market policies. The privacy officer rules this incompatible with the original purpose, so the supermarket asks members for separate agreement and shares only the numbers of those who say yes.