Abstract: Methods, systems, apparatus, including computer programs encoded on a computer storage medium, for providing a publisher with a privacy control UI that enables the publisher to assign one privacy wall to each domain-purpose pair; determining that the publisher has created an additional privacy wall for a specific domain-purpose pair that has an existing privacy wall; in response to determining, restricting the specific domain-purpose pair to a single active privacy wall, including: in response to creation of the additional privacy wall: enabling only one of the existing privacy wall and the additional privacy wall to be in an active state; maintaining any privacy wall that is not in the active state in an inactive state; detecting a transition of a specific privacy wall from the inactive state to the active state; in response to detecting, transitioning a different privacy wall from the active state to the inactive state.