The "brain" of the title is a sophisticated computer[2] with which an anti-communist organisation controls its worldwide anti-Soviet spy network.

Billion Dollar Brain is the third of the Harry Palmer film series, preceded by The Ipcress File (1965) and Funeral in Berlin (1966).

A fourth film in the series, an adaptation of Horse Under Water, also to be released by United Artists, was tentatively planned but never made.

Harry Palmer, who has left MI5 to work as a private investigator, is told by a mechanical voice on the phone to take a package to Helsinki.

In Helsinki, he is met by Anya, who takes him to meet her handler, Harry's old friend Leo Newbigen.

After determining that he cannot trust either Leo or Anya, Harry is abducted by his former MI5 superior, Colonel Ross, who coerces him into working once more for the British government in pursuing the conspiracy and getting the eggs back.

The pair go to Texas, where Harry meets oil tycoon General Midwinter, who proudly displays his billion-dollar "brain", a room full of computers dispensing orders to his agents around the world.

In personnel carriers disguised as his company's oil tanker trucks, Midwinter leads his private army across the frozen Gulf of Finland into Latvia.

Cast notes: Film rights were purchased by Harry Saltzman in November 1965, prior to the novel's publication in January 1966.

Caine narrated a series of Russell's films and became friendly with the director; he recommended him to Saltzman for Billion Dollar Brain.

"[10] In January 1967, it was announced Russell would direct from a script by John McGrath, with Oscar Homolka reprising his role from Funeral in Berlin.

[12][full citation needed][failed verification] Approximately five weeks later, on 26 June, Françoise Dorléac was killed in an automobile accident in Nice, France.

Location filming for Billion Dollar Brain took place in Helsinki and other parts of Finland, including Turku.

To create a relentless, harsh mood, he left out sweet-sounding instruments like violins and flutes and relied mainly on brass and percussion[19] including three pianos, which are featured prominently in the main theme, and later, together with the percussion, create sonorities similar to Stravinsky's Les Noces.

For more romantic moods, it features the ondes Martenot, an early electronic instrument, played by its most prominent soloist, Jeanne Loriod.

Yet, music from the "Leningrad" symphony is featured later on during Midwinter's speech to his soldiers in Finland and during the final battle on the ice.

[22] TV Guide says, "Overly plotted and almost without humor, The Billion Dollar Brain (which takes its name from the computer Midwinter uses to plan his invasion) is not nearly as entertaining as its predecessors in the Harry Palmer trilogy, The Ipcress File and Funeral in Berlin.

[23] Michael Caine thought the visuals were "stunning" but felt "Ken Russell lost the story somewhere and no one could care a damn about what was going on because they couldn't follow what was going on.