What is App Tracking Transparency (ATT)?
App Tracking Transparency (ATT) is Apple's rule, introduced with iOS 14.5 in April 2021, that requires apps to ask users for permission before tracking them across other companies' apps and websites or accessing the IDFA advertising identifier. Most users decline, which sharply reduced targeting and measurement on iPhones and pushed advertisers toward aggregated tools such as SKAdNetwork.
Before App Tracking Transparency, the IDFA was available by default, making cross-app retargeting and attribution easy. Afterwards, apps must show a standard prompt. Opt-in rates vary by app and study, but most analyses show a minority of users agree. Meta said in 2022 that Apple's changes would cost it about $10 billion in revenue that year.
Measurement moved to Apple's SKAdNetwork / AdAttributionKit (now joined by AdAttributionKit), modeled conversions, and first-party data. Regulators in France, Germany and elsewhere have questioned whether ATT unfairly favours Apple's own ads; France's competition authority fined Apple in 2025 over how ATT was implemented.