The Professional Correspondence subseries contains letters to and from Julius Berstl that specifically relate to the business side of writing or theater. His correspondence ranges from publishers, to theaters, to film production companies, and more. The letters range in date from 1943 to the end of Berstl's life in 1975. A majority of the letters within the Profession Correspondence series relate to publishing. Berstl kept a box filled with rejection letters from publishers and theater companies that he received during the last few years of his life (1950s-1970s), which has been transferred to folders.

These letters were mostly found together originally; a small number of other professional letters have been classified under Personal and Biographical Documents or Theater Memorabilia due to their different original location or theme. Individual folder level Scope and Contents notes list the majority of letters found in each folder along with their dates and the people involved.