The correspondence between Herwarth Walden (1878-1941), a gallery owner in Berlin and editor of the avant-garde magazine "Der Sturm," and Wassily Kandinsky (1866-1944) along with his partner Gabriele Münter (1877-1962) spans the brief but artistically vibrant period from March 1912 until the outbreak of World War I in August 1914. The artist group "Der Blaue Reiter," the exhibitions in Walden's Sturm Gallery, and the First German Autumn Salon helped to establish Expressionism and abstraction. This publication now includes, for the first time, all existing letters exchanged between the artists and the gallery owner during these years. The editor Karla Bilang has compiled and extensively commented on these documents over many years. The collection of letters is supplemented by texts from "Der Sturm," written by Kandinsky or others.