The most comprehensive primary source on Van Gogh is the correspondence between him and his younger brother, Theo. Their lifelong friendship, and most of what is known of Vincent's thoughts and theories of art, are recorded in the hundreds of letters they exchanged from 1872 until 1890. Theo van Gogh was an art dealer and provided his brother with financial and emotional support, and access to influential people on the contemporary art scene.
Theo kept all of Vincent's letters to him; Vincent kept few of the letters he received. After both had died, Theo's widow Johanna arranged for the publication of some of their letters. A few appeared in 1906 and 1913; the majority were published in 1914. Vincent's letters are eloquent and expressive and have been described as having a "diary-like intimacy", and read in parts like autobiography.The translator Arnold Pomerans wrote that their publication adds a "fresh dimension to the understanding of Van Gogh's artistic achievement, an understanding granted us by virtually no other painter".