In the 2010s, as cities struggled with economic difficulties following the financial crisis, criticism grew that large companies were not contributing enough through taxes. In 2015, the OECD agreed on reforms to prevent corporate tax planning, and in 2016, the EU adopted a Tax Avoidance Directive that was implemented in Sweden in 2020. Part of the directive focused on tackling double loss relief, where companies and groups were previously able to offset the same loss in several countries, thereby reducing their overall tax burden and achieving liquidity advantages over those operating in only one state. The new rules are complex and difficult to predict in practice because they are based on conditional legislation, i.e. Swedish taxation becomes dependent on how companies are taxed in other states. However, research on these rules is limited, despite the fact that they have a major impact on Swedish companies. The purpose of the study is to investigate and evaluate how the rules work and whether they meet their objectives in a legally secure manner, without unnecessarily hampering cross-border investments or risking violating other EU law commitments, such as the primary law prohibitions on discrimination.