This paper advances the analysis of the concept of Umwelt in Jakob von Uexküll’s work, by examining its different formulations, and highlighting the successive redefinitions of its two components: the perception world and the effect world. Considering the significant impact that the concept of Umwelt had on continental philosophy, the purpose of this study is to reconstruct its meaning through a historical-conceptual analysis, to illuminate some aspects that are not usually thematized in literature—in particular, those related to the effect world.