This book takes a fresh look at understanding how financial markets behave. Using recent ideas from the highly-topical science of complexity and complex systems, the book provides the basis for a unified theoretical description of how today's markets really work. Since financial markets are an excellent example of a complex system, the book also doubles as a science textbook. Contents: 1 Financial markets as complex systems 2 Standard finance theory 3 A complex walk down Wall Street 4 Financial market models with global interactions 5 Financial market models with local interactions 6 Non-zero risk in the real world 7 Deterministic dynamics, chaos and crashes