Apple assigns every Apple Developer Program account a Team ID: a stable 10-character alphanumeric string like `ABCDE12345`. It is the prefix Apple uses to scope every certificate, provisioning profile, App ID, push notification topic, App Group, and iCloud container to your team.
Where you see it
- App Store Connect: under Membership > Team ID.
- Apple Developer portal: in the upper-right account dropdown.
- Inside every provisioning profile (`TeamIdentifier`) and certificate (`OU` field).
- In Xcode build settings as `DEVELOPMENT_TEAM`.
- In `codesign -dvv MyApp.app` output as the second component of the Authority chain (`Apple Distribution: Acme Corp (ABCDE12345)`).
When it matters more than usual
- Universal links and shared App Groups require the same Team ID across every related app and extension.
- Switching teams (acquisitions, contractor handoff) means re-registering every App ID, regenerating every profile, and submitting a Transfer of an App through App Store Connect.
- Shared keychain access between two apps requires they live under the same Team ID.