Indiana University-Purdue University Indianapolis (IUPUI) / This thesis develops a general theory of patterns on the basis of the philosophy of Charles S. Peirce. The main questions with which this thesis is concerned are: what is the ontological status of patterns? In what does their reality consist in? Why does exhibiting patternhood seem to be a necessary condition for the very possibility of cognition? The development of the theory is motivated by a discussion of Ontic Structural Realism (OSR), a theory that has recently been gaining attention in analytic philosophy of science, especially in philosophy of physics. The central claim of OSR is that only patterns (structures) are real; individual objects are not real, or have only a “thin” being in some sense. In this thesis I deal mainly with the version of OSR developed by James Ladyman and Don Ross in their book Every Thing Must Go. I address two criticisms that are commonly levelled against OSR, (1) that it cannot give an adequate account of the difference between physical structure and mathematical structure, and (2) that it cannot give an adequate account of the relationship between the world and our representations of the world. I then show how Peirce’s philosophical framework, as encapsulated in his pragmatism, theory of the categories, Scholastic realism, and theory of the continuum, could provide an answer to these difficulties. OSR will also be used to illuminate an aspect of Peirce’s philosophy which I believe has not been sufficiently emphasized in the literature, namely its structuralist aspect. Specifically, it will be shown that Peirce’s philosophy leads to a worldview very similar to that of OSR, via a path of reasoning that is completely different from those standardly used to argue for OSR. This thesis as a whole is an attempt to throw light on the nature of patternhood through an elucidation and justification of this path of reasoning, which I call the alternative path to OSR.