Genres are commonly used to categorise media artefacts. When using them to map video games, however, one is confronted with challenging follow-up questions: Which of the many criteria, stemming from all sorts of media artworks, are particularly relevant when analysing video game genres? How can they be named and outlined? And how should one handle that they can interactively change and vary depending on player input? This book proposes to understand the idea of video game genre as an impossible taxonomy. It aims to identify how the convolution of countless genre elements within a video game organises itself and how it may be understood as an ever-shifting and flexible phenomenon instead of pursuing the futile ambition of structuring the versatile and fast-developing media corpus. It assembles the required genre theory terms that are applicable to video games, locates their theoretical origin, and documents observations about their interactions with an interactive medium. This chapter offers an introduction to this key idea and an overview of the book’s chapters.