Which of the James Bond films were the most faithful adaptation of the original novels by Ian Fleming?

Doctor No, From Russia with Love and On Her Majesty's Secret Service are perhaps the most faithful adaptations of Fleming's novels. Goldfinger and Thunderball kept the plot, characters and certain important scenes from the books but are otherwise different. When Roald Dahl (yes, him!) was signed on to produce the screenplay for You Only Live Twice, he changed the plot entirely and all that was left from the novel was its' Japanese location and some of its' characters. Diamonds are Forever's plot and characters remained but the story was completely different. This is the same with The Man the Golden Gun, Moonraker and the short stories of For Your Eyes Only and Octopussy. The short stories for A View to a Kill, The Living Daylights and Quantum of Solace bear no resemblance to the films whatsoever. (apart from the sniper scene in The Living Daylights). The novel for The Spy who Loved Me was nothing to do with the film (at Fleming's request as he considered that novel awful). And although a lot of Bond fans will tell you that Casino Royale was a very faithful adaption of Fleming's novel, it really has nothing to do with the novel until we get to the Casino scene. Then it is practically a page for page adaption right until the end of the film. (The characters are also the same)

That's a good question. I actually read a few of Fleming's novels about 25 yrs. ago. - Thunderball, Goldfinger and Diamonds are Forever. Those were very close. Most of his books were written on the 1950's. So anything after like 1972 (the Roger Moore films) the technology changed, and I don't think all the gadgets & weapons were the same as Fleming''s original books.

I never read Casino Royale, but I wonder if the 2006 film was close to the novel.

Seemed like the story was simpler, a love affair, Bond almost poisoned to death,

and the search for the man that his lover worked for.