[Revised entry by Carlo Rovelli on February 4, 2025. Changes to: Main text, Bibliography] Relational Quantum Mechanics (RQM) is the most recent among the interpretations of quantum mechanics that are widely discussed today. It was introduced in 1996, with quantum gravity as a remote motivation (Rovelli 1996); interests has grown since, first very slowly, but steadily, and has peaked during the last years (see Calosi and Riedel 2024, also for a good account of the historical evolution of the interpretation)....