Letters to Family, Friends, and Editors

Letters to Family, Friends, and Editors is a book collecting some of Franz Kafka's letters from 1900 to 1924. The majority of the letters in the volume are addressed to Max Brod. Originally published in Germany in 1959 as Briefe 1902-1924, the collection was first published in English by Schocken Books in 1977. It was translated by Richard and Clara Winston.
Correspondents
Family
Julie and Hermann Kafka - parents
Elli Hermann, née Kafka - sister
Valli Pollak, née Kafka - sister
Ottla Davidová, née Kafka - sister
Josef David - Ottla's husband
Siegfried Löwy - uncle
Other letters to the family are collected in Letters to Ottla
Kafka's long, undelivered Letter to His Father was published separately. It also appears in Dearest Father and The Sons.
Friends
Oskar Pollak - Childhood friend and art historian; a 1902 letter to him includes Kafka's oldest surviving work of fiction - "Shamefaced Lanky and Impure in Heart"
Max Brod - Closest friend; writer and Kafka's literary executor
Elsa Brod, née Taussig - Brod's wife
Sophie Friedmann, née Brod - Brod's sister
Emmy Salveter - Max Brod's friend and possible lover
Felix Weltsch - Classmate; philosopher and Zionist
Lise Kaznelson, née Weltsch - Weltsch's cousin
Irma Weltsch - Weltsch's wife
Oskar Baum - Author, music teacher, and organist
Leo Baum - Baum's son
Robert Klopstock - Close friend, stayed with Kafka through his illness
Romantic Interests
Selma Kohn Robitschek
Hedwig W. - a letter from 1907 includes a poem Kafka claims he wrote "years ago."
Minze Eisner
Tile Rössler
The letters to Milena Jesenská and Felice Bauer are collected in respective volumes. Letters to Felice also includes Kafka's letters to Grete Bloch.
Publishers, Writers and Artists
Ernst Rowohlt - Publisher
Willy Haas - Prague-born writer and journalist, editor of Herder-Blätter magazine
Otto Stoessl - Austrian writer
Kurt Wolff - Publisher
Martin Buber - Philosopher and religious writer
Robert Musil (debatable) - Writer
Alfred Kubin - Graphic artist and illustrator
René Schickele - Alsatian writer and pacifist; editor of Die Weissen Blätter during the war years.
Ernst Feigl - Prague-born poet and writer
Gottfried Kölwel - Poet
Josef Körner - Literary historian and critic
Johannes Urzidil - Prague-born writer and journalist, managing editor of Der Mensch
Julie Wohryzek's sister (unnamed) - Sister of Kafka's former fiancée
Carl Seelig - Writer, critic, and editor (e.g. Robert Walser)
Casual Acquaintances
Director Eisner - Department head at Assicurazioni Generali, where Kafka worked
Gertrud Thieberger - Sister of Kafka's Hebrew teacher, future wife of Johannes Urzidil
Yitzhak Löwy - Actor
Ludwig Hardt - Reciting artist, included some of Kafka's writing in his work
Hugo Bergmann - Former classmate; Philosopher and Zionist
Else Bergmann - Hugo Bergmann's wife
Conversation Slips
Both German and English editions of the book include a selection from the slips of paper Kafka used to communicate during the last few weeks of his life, when he was advised not to speak.
References
Kafka, Franz. Letters to Family, Friends, and Editors. New York City: Schocken Books, 1977.
Essays by Franz Kafka
1959 non-fiction books
Collections of letters
Schocken Books books