In the context of the horizon-problematic, Husserl's notion of the world-horizon occupies a preeminent place: it is the original figure of the horizon in Ideas I—the work that marks the emergence of the horizon-problematic in phenomenology. This chapter traces Husserl's development of the world-horizon in Ideas I with the aim of establishing a rather paradoxical thesis: Ideas I both uncovers and suppresses the concept of the horizon in its all-determining sense. Such is the case because Ideas I both marks the discovery of the world-horizon as well as leaves the problematic of the world-horizon largely undetermined. I further argue that the problematic of the world-horizon is left unexplored in Ideas I because the world-horizon is a specifically genetic notion, which in its first appearance is still dressed in static garb. One can thus say that even though Husserl's Ideas I marks the emergence of the horizon-problematic in phenomenology, this early work procures only a preliminary, and not a conclusive, notion of the horizon.