Abstract: This specification describes technologies relating to displaying online content. In general, one aspect of the subject matter described in this specification can be embodied in methods that include determining a timing penalty for a content item, the timing penalty based in part on weights of previous impressions the content item has been allocated during a plurality of intervals within a delivery period. The methods may further include determining a weight associated with a pairing of the content item and an impression, the weight based in part on characteristics of the impression. The methods may further include determining a score for the content item, based in part on the weight and the timing penalty. The methods may further include selecting one of a set of matching content items, based in part on the score for the content item, and allocating the selected content item in response to a request.

Abstract: Advertisers provide bids for the placement of one or more advertisements on web pages, along with a set of externalities. The externalities from an advertiser indicate discounts that can be applied to their bid based on information learned from a browse history of a user. The externalities may include externalities based on previous viewings of advertisements from the advertiser by the user, externalities based on previous viewings of advertisements from competitor advertisers viewed by the user, and externalities based on web pages or domains that have been visited by the user. When a request for an advertisement is received, the externalities are used to discount the provided bids based on the browse history of the user. An advertisement is then selected based on the discounted bids.