This volume contains the correspondence between the architect, cultural philosopher, and writer Paul Engelmann (1891-1965) and Ludwig Wittgenstein (1889-1951), which spanned from 1916 to 1937, with a longer interruption in later years: a mutually enriching friendship reflected in various thoughts on literature, art, religion, and philosophy. In addition to the letters, excerpts from Engelmann's memories of Ludwig Wittgenstein are also included. The often-cited "unsayable" related to Wittgenstein's philosophy—associated with both art and religion—seems to have been one of the central topics of conversation between the friends. Paul Engelmann not only had the gift of articulating ideas that Wittgenstein found difficult to express, but he also possessed the ability.