Economics is a powerful instrument to understand the current controversial issues on intellectual property: e.g., the extension of patents to software and business models, the lengthening of copyright protection, the compulsory licensing of pharmaceutical products or the legal suits against music downloaders.Economics is also a powerful instrument to improve public policy. It helps to design the appropriate reform to adapt intellectual property law to the 21st century. That is why we wrote this book and decided to deliver it for free. In return of free access to this book, we expect two benefits: useful feedbacks and further diffusion. A digital book can easily be updated and evolve in function of new needs expressed by the reader. We will thus welcome any suggestion that would be worth adding to the book. We especially encourage graduate students and instructors using this textbook to suggest addenda and exercises. We also encourage you to post the weblink to our book wherever it is worth it. This is exactly how internet can be useful! So enjoy the reading, and please diffuse this book!