Dr Federica Liberini is an applied economist and is a Senior Postdoctoral researcher at ETH Zurich and a Research Associate at the University of Warwick. She will be giving a seminar based around her paper ‘The Taxman Calls. How Does Facebook Answer? Global Effects of Taxation on Online Advertising’ co-authored with Angel Cuevas, Ruben Cuevas, Andrea Lassman and Antonio Russo. In the paper the authors study the effects of the taxation of digital platforms on the online advertising market. We exploit novel data on daily unit prices of Facebook ads targeted to country-specific audiences, collected around a major change in the firm’s accounting practices following the introduction of the UK Diverted Profit Tax. They show that a substantial increase in ads prices followed such change, although with heterogeneous intensity across countries. These results are in line with a model of a platform operating in the global advertising market. They show that taxation of profits generated in one country makes the price charged to advertisers from that country (resp. other countries) increase (decrease). Accordingly, they demonstrate that aggregate advertising prices in OECD countries increased more, after the policy change, the larger is the market share of UK-based advertisers.