This document provides an introduction to gamification and outlines the structure of the book. It begins by defining key concepts such as gamification, games, and play. It then introduces the PBL model as the central structure of the gamified system described in the book. The book is organized into 8 levels analogous to game levels, to guide the reader through the process of planning and applying a gamified learning experience. The levels cover elements, mechanics, dynamics, behaviors and how to use the PLEA model to plan a gamified strategy with the goal of motivating students and developing 21st century skills.