Investigating the principle of reasona-bleness in the legal world requires—if the task is to be taken seriously—to take a journey directly to the roots of the concept of law and to the ultimate paradigms that inform its knowledge, just to find the beginning of a different and maybe harder path, heading to the idea of reason. The essays presented in this book do not aim to complete such journeys, but just to take some modest steps into them. Many con-cepts are thereby found, many more are left to be investigated. Meanwhile, between rationality and reasonableness, theory and practice, science and prudence, episteme and phronesis, a global need emerges: that to keep addressing the core of the ‘Rule of Reason’ in the law.