Glossary
What is the IDFA?
The IDFA is Apple's unique, user-resettable device identifier for advertising, which allowed advertisers to attribute ad engagement and installs across apps on iOS.
What the IDFA was for
The IDFA solved a specific problem: recognising the same device at two different moments. An ad network recorded the identifier when a user clicked; the app's SDK recorded it again when the app opened. Matching the two produced a deterministic attribution.
It was designed as a privacy improvement over what preceded it — a resettable, advertising-specific identifier rather than a permanent hardware one, with a user control to reset it at any time.
What ATT did to it
App Tracking Transparency did not remove the IDFA. It gated access to it behind an explicit permission prompt, and most users decline.
The practical effect is the same as removal for most purposes: the identifier is available for a minority of users, and a minority sample cannot be extrapolated reliably because the people who opt in are not a random subset of everyone.
What replaced it is not another identifier but a different measurement model — aggregated, delayed and threshold-gated, through SKAdNetwork and AdAttributionKit.
What still works on iOS
- [IDFV](/resources/glossary/identifier-for-vendor-idfv) for measurement across your own apps, which needs no permission.
- First-party login identity, where the product justifies an account.
- Contextual signals, which never required an identifier.
- Aggregate causal methods — incrementality and MMM.
Common questions
Can I still use the IDFA?
Only for users who granted the ATT permission. Using it without consent for cross-party tracking violates Apple's rules and risks app removal.
Is the Android equivalent affected the same way?
The GAID has remained more available, though Privacy Sandbox on Android is moving in a similar direction over a longer timeline.
More in privacy and compliance
The identifiers, consent signals and rules that bound targeting.