This book introduces a practice-oriented account of how heuristics and cognitive biases shape clinical reasoning and surgical decision-making under uncertainty. Building on behavioral economics and dual-process theory, the authors translate foundational constructs-such as availability, anchoring, confirmation, overconfidence, loss aversion, framing, and survivorship bias-into concrete implications for diagnosis, operative judgment, and multidisciplinary discussions. Drawing on historically grounded clinical narratives, the chapters connect abstract mechanisms to everyday choices in surgery and perioperative care, foregrounding consequences for patient safety and outcomes.  The volume emphasizes awareness, metacognition, and deliberate "choice architecture" in the operating room and clinic, culminating in general and context-specific checklists for bias mitigation. While not a comprehensive taxonomy, the book provides a structured entry point for surgeons and trainees seeking to improve decision quality, reduce diagnostic error, and design safer systems.  The original manuscript of this book was written in Spanish and translated into English with the help of artificial intelligence. A subsequent human revision was done primarily in terms of content.