The broad involvement and diversity of products within the European Emissions Trading Scheme (EU ETS) has been important in driving liquidity and market efficiency and has itself fuelled further market growth. But as the EU carbon market has grown in size, value and complexity it has become an increasingly attractive playground for fraudsters. Fraud has materialised on this market in a variety of sophisticated forms, including Value Added Tax (VAT) carousel fraud and emissions allowance thefts. In recognition of specific vulnerabilities within the EU ETS trading system, significant changes to the way that emissions allowances are traded were introduced to the Registry Regulation in 2013, as well to the EU financial markets regulations in 2012–2014, in an attempt to strengthen the EU ETS against financial crimes. This chapter examines the major forms of fraud that have affected the EU ETS, and highlights specific characteristics of emissions allowances and the registries system through which they are traded that have made the EU ETS especially vulnerable to fraud. Moreover, it discusses the regulatory reforms that have been implemented at both EU and national levels to address these vulnerabilities.