The Khitomer Accords were a series of peace treaties signed in 2293 between the United Federation of Planets and the Klingon Empire that put an end to years of hostility between the two powers. The treaties were originally planned to be signed on Earth but due to the assassination of Klingon Chancellor Gorkon, the conference was relocated to Camp Khitomer on the planet Khitomer. The turning point in Federation-Klingon relations was brought on by the explosion of Praxis, a Klingon energy moon, which directly threatened the habitability of Qo'noS, the Klingon homeworld. At the time of the explosion, it was thought that the Empire only had fifty years of life left.
The Accords were nearly stopped by a conspiracy of officers and officials from the Federation and Romulan and Klingon Empires who assassinated Gorkon, but officers from the USS Enterprise-A and USS Excelsior uncovered the conspiracy and apprehended those responsible before they could assassinate Federation President Ra-Ghoratreii. (Star Trek VI: The Undiscovered Country, VOY: "Flashback")
After the formation of the Typhon Pact in 2381, Federation President Nanietta Bacco and Klingon Chancellor Martok sought to expand the scope of the Accords, bringing in other allies like the Ferengi Alliance, Cardassian Union, and possibly the Talarian Republic. (ST novel: A Singular Destiny)
In 2385, Commander Vrelek of the Romulan Home Guard admitted to USS Cole commanding officer Stu Karsten and Chief Medical Officer Doctor Henglaar that the Romulan Star Empire had signed the Second Khitomer Accords, which prohibited use of subspace weapons against other signatories like the Federation and Klingons, but it did not prohibit the Romulans from using those types of weapons against non-signatories like the Archein. Karsten stated the Accords did, however, require all signatories to destroy all existing subspace weapons: something the Romulans obviously had not complied with. (Henglaar, M.D.: "Profit Without Honor")