This chapter draws on our two studies published by the International Centre for Tax and Development (ICTD), using the two leading datasets on the global activity of multinational enterprises (MNEs). The approaches are complementary but necessarily distinct, given the difference in available data. We summarise the approaches taken, and the specific findings that emerge from each, and then highlight three major common results. First, notwithstanding uncertainty and data issues, this is a first-order problem in relation to the world economy. Second, the overall effect of a switch to unitary taxation, almost regardless of the actual apportionment formulas used, would be a substantial redistribution from MNEs towards most countries of the world. Only a handful of jurisdictions would see significant revenue losses, and these are far outweighed by the gains of all others. Third, there are significant differences in the extent of redistribution implied by a global apportionment approach relying on different factors – with corresponding implications for the development impact of given global choices, and/or for unilateral decisions at regional and national level. Overall, the findings confirm the critical importance of improving the available data. In doing so, they underline the failure of the OECD base erosion and profit shifting (BEPS) process to deliver on commitments in this area, but also highlight the potential of using the newly-required country-by-country reporting data of MNEs. A specific proposal for a data registry is put forward.