Abstract: An online system is described that utilizes an extranet or intranet for the selection and purchase of digital advertising media, and the creation, distribution and management of media content. The invention comprises a methodology for presenting an online marketplace that brings together advertisers and media owners with available advertising inventory by providing a dynamic inventory of advertising space that is available for users to display digital advertisements; presenting through one of a plurality of portals a user interface through which a user may build a digital advertisement for use on one or more of the available advertising spaces within the inventory; and causing the created advertisements to be displayed on one or more of the available advertising spaces within the inventory.