This chapter aims to introduce the reader to the central themes explored in the next 12 chapters. With this in mind, the chapter draws a distinction between the horizon as an everyday word and the horizon as a philosophical concept. The chapter also provides a brief philosophical history of the horizon by tracing how this notion has been employed starting with the Liber de causis and ending with Nietzsche and Dilthey. I argue that despite the various ways in which the notion of the horizon has been employed in the history of philosophy, Husserl was the first to provide this notion with a specifically philosophical determination. The chapter shows how the notion of the horizon is to be conceived as a phenomenological notion as well as clarifies how the question of origins is to be understood in the subsequent analysis. Finally, the chapter clarifies the structure of the following investigation and explores the motivating factors that underlie an inquiry into the origins of the horizon.