Foreign Relations of the United States, 1969-1976, Volume XLII, Vietnam: The Kissinger-Le Duc Tho Negotiations
https://history.state.gov/historicaldocuments/frus1969-76v42
Includes a complete set of the memoranda of conversation between Kissinger and North Vietnamese Politburo member, Le Duc Tho. Covers the evolution of U.S and Vietnamese negotiating positions, the agreement on the Accords, and how the aftermath failed to lead to a political settlement of the war. From the State Department