In the September issue of the Journal of Advertising Research, the Advertising Research Foundation (ARF) introduced its "How Advertising Works" research initiative (Stipp, 2016), which combines original experiments with outside research. The goal: to offer practical guidance for improving advertising effectiveness- and the return on investment (ROI) for marketing spend-in an increasingly complex, multimedia world. In the pages that follow, we offer the first of a series that explores the methodology of the latest investigations of cross-platform advertising effectiveness. Here, ARF executive researchers Jasper Snyder and Manuel Garcia-Garcia describe their study of the conditions under which inserting multiple platforms in a campaign leads to specific advertising effects. The evidence overwhelmingly points to higher ROI from advertising on multiple platforms than advertising on a single platform only, with the most powerful results coming from reinforcing television with digital strategies. Next on their agenda: understanding the creative drivers that make an execution successful in mobile platforms. © 2016, World Advertising Research Center. All rights reserved.