This book examines how cyber-currencies, currencies which only exist in electronic form and generally require online transmittal, fit into existing legal frameworks. Using the English legal system as a basis, but drawing upon other major jurisdictions such as the USA and Switzerland, the book analyses how public and private law accommodates existing and emerging forms of electronic currency. The book starts with a consideration of the definition of money, including the status of currency issued by the state or operating through intermediated payment systems. Fundamental questions regarding issues of ownership, transferral and taxation are addressed with a view to equipping the reader with the tools to answer common transactional questions about cyber-currencies.