Charles Sanders Peirce (b. 1839–d. 1914) was a polymath who contributed many insights to diverse sciences, from cartography to photometry, from mathematics to metaphysics, and from linguistics to psychology. His fields of philosophical interest cover logic, ontology, epistemology, ethics, aesthetics, metaphysics, history, and the philosophy of religion. Today, he is recognized as the founder of the philosophy of pragmatism. Besides being a scientist, logician, and philosopher, Peirce is the patron of modern semiotics, which is the core of his philosophical system. Logic conceived as semiotics, and semiosis, defined as the agency of the sign, are key concepts of his philosophical architecture. The sign, in turn, is a synonym of thought, mind, and continuity. Semiotics, according to Peirce, is founded on phenomenology, whose three universal categories are at the root of his philosophical system. Logic or semiotics is not isolated but coordinated within two other normative sciences, ethics and aesthetics, which guide human ideals. The interconnections between these three branches of philosophy are essential to Peirce’s evolutionary pragmatism. Peirce’s insistence on the principle of continuity as well as evolutionism tout court lies in the two cornerstones of his metaphysics, synechism, the doctrine of continuity, and its complementary opposite, tychism, the doctrine of absolute chance. In the philosophy of science, his corresponding doctrine is the one of fallibilism, which postulates that our knowledge is never absolute but always swims in a continuum of uncertainty and indeterminacy. Fortunately, the times when Peirce’s originality was considered a symptom of incoherence have passed. Years of competent scholarship testify to the contemporary relevance of his genius.