Charles S. Peirce (1839-1914) was, perhaps, first and foremost a practising or experimental scientist. However, Peirce was also a philosopher, and to him the relation between science and metaphysics was intimate. Peirce not only wanted to develop a metaphysical system consistent with the important scientific results and conceptions of his time, but also, like Immanuel Kant, to set metaphysics on the path of a science. This collection of articles investigates central themes and difficulties in the metaphysics of Peirce ― some of the articles clarify aspects of his metaphysics, others also show their contemporary relevance. The essays fall under the different headings of ontology, psychical or religious metaphysics and, finally, physical metaphysics.