Online companies are central to how Europeans access information, communicate and receive services in the digital economy. This includes platform companies such as Uber and Deliveroo in mobility and food delivery, Upwork in freelancing and Airbnb in accommodation. Yet despite their popularity, online companies are often criticised for business practices that users, workers and other businesses consider unfair, particularly because these platform participants have little choice but to accept the platforms’ rules. An online marketplace might have unclear pricing or hidden fees, or a social media company may rely on opaque and misleading algorithms, making it difficult for users to understand why certain content is shown or hidden.This guide focuses on fairness and provides recommendations for managers of platform companies on how to make their platform business models fairer towards participants: users, workers and other businesses. There is still room for interpretation regarding what is fair and what is not. By fairness, we mean the idea that companies should implement practices that are attentive to the needs and perspectives of all participants on the platform. This publication is an introduction to the topic and draws on best practices from the field. Managers of platform companies can use it for internal discussions, to reflect on their own business models and to sharpen their own understanding of fairness.The report draws on three years of research within the EU Horizon project "INCA – Increase Corporate Political Responsibility and Accountability of Digital Platforms", including interviews with managers of 15 European platform companies in Germany, Italy and Spain. Its findings are also directly relevant for companies preparing for the European Digital Fairness Act (DFA), currently under development, which will establish a legal basis for preventing unethical, misleading and exploitative commercial practices.