Since 2016, most large multinational companies have been required to submit country-by-country reports, detailing the distribution of their economic activity, reported profits, and taxes paid in each jurisdictions in which they operate. Each MNE reports this data to the tax administration of its headquarter country which then shares this information with the tax administrations of all countries in which that particular MNE operates. This data is not made available to the public at the company-level, only at the aggregate level as part of the OECD Corporate Tax Statistics (at least until late 2025). However, in recent years, several research teams have collaborated with tax administrations (in France, Italy, Germany, and Slovakia) to analyze this confidential data to assess the potential impact of proposed reforms, quantify the scale of misalignment of economic activity and reported profits, and in general analyze the behaviour of multinational companies. In this session, we review the lessons learned from these efforts.