A set of content items, such as web pages, are identified in response to a query generated by a user. The Identified content items are initially ranked using a ranking scheme. User-interaction data that describes preferences that the user may have towards some of the ranked content items is received. In order to personalize the ranking of the content items for the user, the user-interaction data is used to re-rank the ranked content items in a way that favors content items that are preferred by the user, while also preserving the initial broadly applicable ranking with respect to content items that are not preferred or that are equally preferred by the user.