The aim of this study is to identify and explicate Nietzsche’s standard of value, that is, the basis upon which he approves of some human phenomena (e.g., moralities, philosophies, artistic and political movements, etc.) and disapproves of others. I argue that this standard is best captured by the concept of “degrees of strength.” Part I undertakes a detailed examination of Nietzsche’s philosophical methodology, which must be understood in order to understand his conception of degrees of strength. I argue that the central tenet of his methodology is his commitment to “historical philosophy,” that is, to the view that absolutely opposite phenomena like soul and body, good and evil, and so on, do not exist as opposites, and that their opposition is only relative. I here engage with what is perhaps the most prominent reading of Nietzsche’s methodology in the Anglophone world today, namely that it is a form of “naturalism,” understood as a commitment to some kind of continuity with the empirical sciences. I show that this reading relies on a definition of “nature” that Nietzsche never gives, and commits him to an ontology that he explicitly rejects, without doing anything to clarify his methodology that is not done by the concept of historical philosophy. Part II examines Nietzsche’s attempt to formulate a “proper physio-psychology” based on historical philosophy, which requires him to conceive of human beings as communities of willing subjects that he calls “drives.” I argue that Nietzsche adopts the notion of the human being as a multiplicity from physiology, and attempts to combine it with the notion of the willing subject that arises from introspective psychology. He believes that the human belief in causality is a result of the psychological experience of willing, and that physiology cannot explain the causal relations among events in the body without appealing to a concept of will. I then show how he extends this insight beyond the body to the world as a whole, arguing that we cannot comprehend causality at all except by means of the concept of “will to power.” This, I claim, is Nietzsche’s main reason for asserting that the world is “will to power and nothing else.” Part III introduces Nietzsche’s concept of the “problem of value,” the solution of which amounts to what he calls “the determination of the order of rank among values,” that is, of which human values contribute most to the enhancement of the power of humanity, and which frustrate such enhancement. I argue that the standard by which Nietzsche determines this is a symptomatology based on the concept of degrees of strength: those “ways of thinking and valuing” that are symptomatic of higher degrees of physio-psychological strength are more valuable for the enhancement of the overall power of humanity, while those that are symptomatic of weakness are less valuable, or even disvaluable, for that end. While the main focus of Part III is to explicate the concepts of physio-psychological strength and weakness, I conclude with an examination of what Nietzsche calls the “great economy of the whole,” according to which even weakness often has value for enhancing the power of humanity, so long as it is kept in its proper place and not valued more highly than strength. / Dissertation / Doctor of Philosophy (PhD)