Devising an optimal tax scheme for international business transactions within the scope of law and the guaranteed freedom of contract is a legal instrument of international tax planning. However, experiences show that taxpayers are well-advised to document the principles of intra-company transfer pricing in due time. The OECD Transfer Pricing Guidelines provide a lead as to which issues may prompt fiscal administrations to instigate tax audits (running losses, market strategies, unhedged exchange or interest rate changes, etc.). Martin Hummer gives an overview of transfer pricing documentation in international business against the backdrop of ever-tightening country-specific requirements, and explains the masterfile concept within the European Union.