Hermann Weyl (1885–1955) is one of the most significant mathematicians and theoretical physicists of the past century. His work is strikingly inspired and permeated by broader philosophical considerations. He understands the inner mathematical debate surrounding intuitionism and formalism in terms of a confrontation between Husserlian phenomenology and Fichtean constructivism. He describes coordinate systems as necessary residues of self-dissolution and, through the concept of the infinite, referencing Meister Eckhart and Nicholas of Cusa, he demonstrates connections between theology and mathematics. He examines the mathematician's engagement with symbols using Heideggerian concepts, and in the course of establishing general relativity and quantum mechanics, he draws on a Leibnizian theory of matter, which he attempts to integrate into a historical dialectic of the modern concept of matter, in line with German idealism. Norman Sieroka illustrates the interconnections and the unity of all these considerations in his book. Whether it concerns mathematics, physics, subjectivity, or symbol theory, Weyl always varies a concept of activity that relates to a specific form of environment. A person constitutes themselves through their activity, their actions, in social environments; matter produces physical effects in a spacetime environment. It is the structural analogies that characterize and connect Weyl's considerations. This reconstruction is made possible by a historical examination of Weyl's own academic environment, particularly the intense interaction with the philosopher Fritz Medicus. Thus, the concept of environment is not only contentually but also methodologically central to a work that claims scientific-historical and philosophically systematic relevance.