100th edition announcement.- Authors Biographies.- Introduction; Damiano Canale & Giovanni Tuzet.- 1. Looking for the Nature of Law: On Shapiro's Challenge; Damiano Canale.- 2. The Possibility Puzzle and Legal Positivism; Francesca Poggi.- 3. What is Wrong with Legal Realism?; Giovanni Tuzet.- 4. Rule of Recognition, Convention and Obligation. What Shapiro Can Still Learn from Hart's Mistakes; Aldo Schiavello.- 5. Legality: Between Purposes and Functions; Diego Papayannis.- 6. What Can Plans Do for Legal Theory?; Bruno Celano.- 7. Ruling Platitudes, Old Metaphysics, and a Few Misunderstandings about Legal Positivism.; Pierluigi Chiassoni.- 8. Theoretical Disagreements. A Restatement of Legal Positivism; Jordi Ferrer and Giovanni Battista Ratti.- 9. 'What's the Plan?' On Interpretation and Meta-interpretation in Scott Shapiro's Legality; Giorgio Pino.