The global fight against tax evasion has been one of the major success stories of international co-operation over the past decade, leading to new global transparency standards and more than 100 billion euros in additional revenues for countries worldwide. To mark the 10th anniversary of the Global Forum on Tax Transparency and Exchange of Information for Tax Purposes, which brings together more than 150 countries, former UK Prime Minister Gordon Brown explains how the G20 launched the crackdown on bank secrecy and tax evasion, and the challenges that remain.