Among other things, publishers of digital content are enabled each to define, for each of one or more digital content items, a style in which the digital content item is to be presented to a user and a condition under which the user may have the digital content item presented. The digital content items are stored in a content library, the styles and conditions associated with the digital content items are stored in a server. Each of the digital content items is enabled to be presented to users within presentation contexts that are accessible to the users and controlled by presentation context providers. The presentation of the digital content items includes obtaining the digital content items from the server and controlling the presentation to occur under the conditions and in the styles defined by the publishers.