The correspondence is an intellectual and moving document of a friendship between two scholars. It unfolds in 115 letters from 1983 until Feyerabend's death in 1994. The letters are accompanied by a foreword, an introduction by Hoyningen-Huene, and biographical notes from the editor. Both correspondents are convinced that science discovers something about the world – they humorously, profoundly, and at times sarcastically reflect on criteria and methodology. The correspondence bears witness to a deep and vibrant friendship and is more than just an emblem of the philosophy of science at the end of the last century. Previously unpublished source material serves as the basis for the editor's biographical comments.