IDFA

IDFA stands for Identifier for Advertising, a device‑level random identifier assigned by Apple to iOS devices to enable advertisers to track and profile users for advertising and attribution.

It is used to deliver personalized ads, measure ad performance, frequency capping, and cross‑app and cross‑site attribution. The IDFA is accessed by apps through Apple's AdSupport framework and can be reset by the user at any time in Settings. It is distinct from other device identifiers and remains separate from the user's Apple ID.

Privacy changes have significantly affected how the IDFA is used. Since iOS 14, App Tracking Transparency requires apps to obtain user permission to access the IDFA for cross‑app tracking. If permission is not granted, the IDFA is restricted or not accessible, and advertisers rely more on privacy‑preserving methods such as Apple's SKAdNetwork for attribution.

Impact and usage continue to evolve in response to policy and user expectations. While the IDFA remains a common tool in mobile advertising, its availability has decreased due to consent requirements and stricter privacy standards. Advertisers often rely on first‑party signals, probabilistic modeling, and publisher data, or on Apple’s privacy‑preserving attribution options.

Related identifiers include the Identifier for Vendor (IDFV), which is scoped to apps from the same vendor. The IDFA and associated privacy changes reflect a broader shift toward user privacy in mobile advertising.