By using algorithms, digital platforms have been able to develop new business models that have enabled them to break into most sectors of the economy: transport (Uber, BlaBlaCar), short-term property rental (AirBnB, Séjourning), online sales (Amazon, Ebay), etc. However, these platforms do not always behave fairly (abuse of a dominant position and unfair competition between them, asymmetric information in their relationship with their users, etc.). However, these platforms do not always behave fairly (abuse of dominant position and unfair competition between them, informational asymmetry in their relationship with their users, etc.). It was as a result of this observation that the French legislator, in order to protect the citizens who use the said platforms, imposed a principle of fairness on digital platforms through Act no. 2016-1321 of 7 October 2016 for a Digital Republic. What is this principle called? Why is it important? What are the procedures and difficulties involved in implementing it? This book attempts to provide answers to these and other questions. The book also highlights the various methods of regulation used - and yet to be used - by the public authorities to "discipline digital platforms.