This edition includes the letters exchanged between Charles S. Peirce and the Open Court Publishing Company between 1890 and 1913. Open Court published more of Peirce’s philosophical writings than any other publisher during his lifetime, and played a critical role in what little recognition and financial income he received during these difficult, yet philosophically rich, years. This correspondence is the basis for much of what is known surrounding Peirce’s publications in The Monist and The Open Court—two of the publisher´s most popular forums for philosophical, scientific, and religious thought—and is therefore referenced heavily in Peirce editions dealing partly or wholly with his later work, including The Essential Peirce series and Writings of Charles S. Peirce. The edition provides for the first time a complete text of this oft-cited correspondence, with textual apparatus, contextual annotation, and careful replications of existential graphs and other complex illustrations. By so doing, this edition sheds critical light not only on Peirce and Open Court, but also on the context, relationships, and concepts that influenced the development of Progressive Era intellectual history and philosophy.