This open access book introduces the first systematic approach to the debate on the unity or fragmentation of practical reasoning and its profound implications for legal philosophy. Bringing together some of the foremost legal philosophers from the Hispanic-Latin world, the book presents a thoughtful dialogue with the Anglo-American literature, making it of interest to scholars from both cultural traditions. Although the topic is rarely discussed explicitly and systematically, it is pivotal to ongoing debates about legal normativity, the nature of law, legal authority, and the rationale behind legal decisions. This book fills this gap by providing a comprehensive perspective that illuminates the intersections between the philosophy of law and the philosophy of practical reasoning. It analyses law from the perspective of the agent and offers deep insights into critical issues in the field of law. The volume is divided into four parts. The 1st part addresses the question of the nature of reasons and the unity of practical and theoretical reasoning. The 2nd part deals with the question of whether practical reasoning works in a unified or fragmented way. The 3rd section examines the autonomy of legal normativity in relation to morality and other normative domains. In the 4th and concluding section, the authors analyse the implications of the thesis of the unity of practical reason for legal decision-making and the authority of law. The ebook editions of this book are available open access under a CC BY-NC-ND 4.0 licence on bloomsburycollections.com.