Privacy & regulation · also called ATT
App Tracking Transparency (ATT)
App Tracking Transparency (ATT) is Apple's framework, introduced with iOS 14.5 in 2021, requiring apps to ask users' permission before tracking them across other companies' apps and websites or accessing the IDFA.
Since April 2021, any iPhone app that wants to track users, meaning linking data from its app with data from other companies for targeted advertising or measurement, or sharing it with data brokers, must first display Apple's standard prompt asking the user to allow tracking. If the user says no, the app receives a zeroed IDFA and must not track by other means such as device fingerprinting.
Opt-in rates have varied by app and category but have been well below the pre-ATT norm, making iOS audiences much less addressable. The biggest impact fell on mobile app install advertising and on platforms that depended on cross-app data. Advertisers shifted to Apple's privacy-preserving attribution, SKAdNetwork and AdAttributionKit, plus modelled measurement, first-party data and contextual signals.
ATT has also drawn competition scrutiny. Regulators in several countries, including France, Germany and Italy, examined whether Apple applies the rules to itself on equal terms; France's competition authority fined Apple €150 million in March 2025 over how ATT was implemented.
Think of it like this
ATT is like a building rule that no one may follow residents from building to building unless each resident personally signs a permission slip.
An example
A shopping app in the UK shows the ATT prompt; 30% of users allow tracking. For the other 70%, the app's ad campaigns are measured with aggregated AdAttributionKit postbacks.
Related terms
IDFA
IDFA (Identifier for Advertisers) is Apple's resettable advertising identifier for iPhones and iPads, which apps can access only if the user grants permission through App Tracking Transparency.
SKAdNetwork / AdAttributionKit
SKAdNetwork and its successor AdAttributionKit are Apple's privacy-preserving frameworks that tell advertisers which ad network drove an iOS app install, without revealing user-level identity.
Signal loss
Signal loss is the reduction in data available to target, measure and optimise advertising, caused by browser cookie blocking, mobile ID restrictions, privacy laws, consent choices and ad blocking.
Mobile advertising ID (MAID)
A mobile advertising ID (MAID) is a resettable identifier that a phone's operating system provides for advertising, such as Apple's IDFA or Google's GAID, letting apps recognise the device for ads.
MMP (mobile measurement partner)
An MMP (mobile measurement partner) is an independent company that attributes app installs and in-app events to the ads and ad networks that drove them, and detects mobile install fraud.
Sources: Apple Developer: App Tracking Transparency, Apple: User privacy and data use, Apple Developer: advertisingIdentifier