Tie Breaking Rules For Content Item Matching

Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for selecting controlling keywords. In one aspect, a method includes determining that two or more targeting keywords for a same content item source are matched by one or more terms in a content item request, where a first targeting keyword matches the one or more terms with a more specific type of match than the second targeting keyword. If the bid associated with the second targeting keyword does not exceed the bid associated with the first targeting keyword, the first targeting keyword and the second targeting keyword are ranked based on selection scores. The targeting keywords are ranked based at least in part on the quality scores when the bid associated with the second targeting keyword does exceed the bid associated with the first targeting keyword.