Casino Royale is not the first adaptation of that Bond novel. A TV movie was made in the '50's, Americanising it, and a spoof version starring David Niven (ironically, Fleming's first choice for Bond) was made in the '60's.
Surprisingly, many elements from the novel made it in, although many details and setpieces were changed. In the novel, Le Chiffre and Bond play baccarat, or rather chemin de fer. Leiter is introduced to Bond earlier. Vesper Lynd is the secretary of the Station of MI6 relating to the USSR, and Le Chiffre is one of the foreign treasurers for the USSR. His name is given a background, as he was found in a concentration camp (although whether he was maybe a collaborator or a prisoner was never established), and had only a number on a passport. So his aliases became variations on 'number' or 'cipher'.
Le Chiffre is financing the left-wing unions in France, but invested the money in a chain of brothels and porno theaters, only to have the French Government enact 'la Loi Marthe Richard', which effectively closes him down and loses his money.
The main villains are the Russian counteritelligence group SMERSH (Smiert Shpionam, or 'death to spies'), here portrayed as a death-squad against Russian enemies. IRL, SMERSH had been absorbed into various intelligence agencies after WWII, and was all but disbanded not long after Fleming wrote this. In the movie, SMERSH is replaced by an unnamed terrorist organisation, which has been rumoured to be a new version of SPECTRE.
In the book, instead of being poisoned by digitalis, Bond is threatened by one of Le Chiffre's cronies with a gun concealed in a walking stick. The beating Le Chiffre gives to Bond is with a bamboo carpet beater (basically an oversized flyswat), and is in a villa. Finally, in the novel, Vesper kills herself with an overdose of pills after spotting an assassing with an eyepatch, Gettler.
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