The Blofeld Trilogy (also known as the SPECTRE Trilogy) is a three volume story arc written by Ian Fleming between 1961 and 1964.
The trilogy centres around the villainous SPECTRE organization, and its leader Ernst Stavro Blofeld. The novels are: Thunderball (1961), On Her Majesty's Secret Service (1963) and You Only Live Twice (1964).
In addition, in The Spy Who Loved Me (1962), both SPECTRE and Blofeld referred to briefly by Bond, however this novel is generally not considered part of the arc. The Man with the Golden Gun (1965) contains the final mentions of Blofeld and effectively picks up where You Only Live Twice ended. While some regard this novel to be included as a part of a "quadrilogy", it is mostly seen as including merely a postscript of the Blofeld/Spectre trilogy.