The tax treatment of intellectual property is currently in the spotlight and there is considerable interest in understanding how taxes affect firms' choices over where to hold patents for tax purposes. In a forthcoming paper, we estimate the responsiveness of European multinationals' patent holdings to corporate taxes. We consider firms' decisions over which subsidiary to hold each of their patents in. This choice is crucial for determining the jurisdiction under which the patent income will be taxed. We consider taxes in the country where intellectual property is held as well as interactions with taxes in the home country via CFC regimes. We simulate the effects of introducing Patent Boxes, in terms of both the location of income and the resulting government revenues, under alternative assumptions about how CFC regimes will interact with Patent Boxes. This Briefing Note summarises the main results from that paper (Griffith, Miller and O'Connell, 2010) and discusses our findings in relation to the current policy issues.