The source novel "The Berlin Memorandum" is billed in the credits as being by Adam Hall. This is a nom de plume for author Elleston Trevor.
Even though this movie was made over twenty years after the end of World War II, the devastation of Berlin was so vast, the set decorators weren't required to "re-create" exterior areas for filming, just interiors.
In adapting (Elleston Trevor writing under his nom de plume) Adam Hall's novel "The Berlin Memorandum", screenwriter Harold Pinter altered the emphasis of the book to be less a spy thriller and more a meditation on the human condition and the duplicitous nature of identity.
The score was composed by John Barry, who became notable for the early James Bond spy movie soundtracks. Barry composed the score for this movie between "Thunderball (1965)" and "You Only Live Twice (1967)."