Hilary Putnam is often described as a thinker with constantly changing philosophical views. The evolution of his thought is common divided into three periods: metaphysical realism, internal realism, and common-sense realism. However, Putnam did not elaborate and defend three different and opposite philosophical systems. Putnam has never been a system builder, but rather a truly analytic philosopher who attempts to resolve particular philosophical questions and not to develop a comprehensive worldview. The paper focuses on particular philosophical issues discussed by Putnam in the philosophy of mathematics, ontology, the philosophy of language, the philosophy of mind, and the theory of truth. It becomes clear how little Putnam’s approach has changed during his lifetime. A striking feature of his approach is realism which, irrespective of different qualifying adjectives in different periods, gives an underlying unity to his philosophy.