The purpose of this study is to assess Husserl’s debt to Lotze’s philosophy during the Halle period (1886-1901). I shall first track the sources of Husserl’s knowledge of Lotze’s philosophy during his studies with Brentano in Vienna and then with Stumpf in Halle. I shall then briefly comment on Husserl’s references to Lotze in his early work and research manuscripts for the second volume of his Philosophy of Arithmetic. In the third section, I examine Lotze’s influence on Husserl’s antipsychologistic turn (...) in the mid-1890s. The fourth section is a commentary on Husserl’s manuscript entitled “Microcosmus,” to which he explicitly refers in his Prolegomena, and which he planned to publish as an annex of his Logical Investigations. This work contains a detailed analysis of the third book of Lotze’s 1874 Logic. The last section examines Husserl’s arguments against logical psychologism in his Prolegomena, which I discuss through the lens of Stumpf’s critique of psychologism in his paper “Psychology and theory of knowledge”. I argue that Stumpf’s early works on this topic make it possible to establish a connection between Lotze’s interpretation of Plato’s theory of Ideas and Husserl’s antipsychologism. My hypothesis is that Stumpf’s analyses represent the background of Husserl's critique of logical psychologism in his Logical Investigations. I shall conclude this study by showing that Husserl’s position with respect to Lotze’s philosophy remains basically unchanged after the publication of his Logical Investigations, and that Husserl’s main criticism of Lotze pertains, in the final analysis, to the absence of a theory of intentionality in Lotze’s philosophy. (shrink)