The book does what the title says: a practitioner textbook on the economic principles of competition law, targeted specifically at competition lawyers (be they solicitors, barristers, in-house counsel, lawyers at government agencies, or judges). It is written in the language and tone of an economic expert report to a court: taking the reader back to first economic principles, through to the application of those principles to competition cases. The book covers all the main topics in competition law where economics is relevant: market definition, market power, abuse of dominance, cartels, and other horizontal agreements, vertical agreements, and mergers. It also discusses the less familiar areas of remedy design and damages, and explains the basic principles of game theory, behavioural economics, econometrics, and financial analysis. Each topic is introduced by asking questions based on real-world cases from jurisdictions around the world. A theme throughout the book is how economics can help with the application of competition law in new challenging areas such as markets characterized by consumer biases, digital and online markets, and the interface between IP and competition law. The book ends with a discussion of best practice in the use of economic evidence and economic experts in competition cases before competition authorities and courts.