This paper considers the structure of advertising effectiveness on the internet. It investigates empirically the importance of creative and media factors for banner effectiveness. Econometric modelling of actual data on banner ads demonstrates that creative factors such as banner size, animation, message length and logos, as well as media factors such as campaign length, number of host websites, use of offline media, and campaign cost, may influence the direct response of the target audience as measured by click-through rates. The results lead to important practical implications for internet advertising.