The Manuel Mujica Láinez Papers consists of working and personal papers of the Argentinian novelist, short story writer, biographer, and essayist Manuel Mujica Láinez. The papers primarily contain correspondence he received from Argentinian and Spanish writers (1927-1984), as well as family correspondence (1901-1984). Also included are a few manuscripts by Mujica Láinez, several poems (some dedicated to Mujica Láinez) and non-fiction manuscripts by others, and manuscripts of conference papers. The strength of the collection is the documentation of Mujica Láinez's literary career, beginning with a letter received from poet Alfonsina Storni in 1927 and continuing with many letters acknowledging the publication and critical reception of Mujica Láinez's writings. The critical response to his novel Bomarzo, first published in 1962, and public controversy over the prohibition of staging the opera Bomarzo at the Teatro Colón in Buenos Aires in 1967, are particularly well-documented in the letters received by the author.

Correspondents represented in the collection include many writers who have figured prominently in twentieth-century Argentinian literature, such as Jorge Luis Borges, Victoria Ocampo, Silvina Ocampo, Adolfo Bioy Casares, Silvina Bullrich, Enrique Larreta, Eduardo Mallea, and Ricardo Rojas. In addition to novelists, Mujica Láinez corresponded with many poets and critics, including Gabriela Mistral, Bernardo Canal Feijóo, Enrique Pezzoni, Eduardo González Lanuza, Alejandra Pizarnik, Olga Orozco, Alberto Girri, and Alberto Manguel. European writers represented in the collection include Spanish authors Ramón Gómez de la Serna, Américo Castro, Luis Antonio de Villena, and Guillermo Carnero, French biographer André Maurois, novelist Joseph Kessel, and Swiss author Denis de Rougemont.

The few manuscripts by Mujica Láinez include an autograph essay on Victoria Ocampo, "Victoria Argentina," which was written for a commission formed to honor her ("Comisión de Homenaje a Victoria Ocampo"), and a draft speech by Mujica Láinez, honoring Victoria Ocampo in December 1965. The manuscripts written by others include two poems by Alberto Girri, and poems (one each) by Luis Antonio de Villena and Oscar Hermes de Villordo. Among the letters sent to Mujica Láinez, there are two letters about the suicides of two well-known Argentinian poets: one, by Alberto Gerchunoff, on Leopoldo Lugones' death in 1938; and the other, by Alberto Manguel, on Alejandra Pizarnik's death in 1972.

The family correspondence includes both letters written by and to Mujica Láinez, and letters written between other family members. (To assist with identification of other family members, their relationship to Mujica Láinez is included in brackets after their names. Refer also to the family tree in the Biographical Sketch section.) Mujica Láinez corresponded extensively with Ana de Alvear de Mujica Láinez ["Anita"] [wife], Lucía Láinez de Mujica Farías ["Chía"] [mother], Ana Mujica [daughter], and Justa Varela de Láinez ["Lala"] [grandmother]. A large portion of the correspondence of the other family members consists of letters between Lucía and Manuel Mujica Farías [father], and letters between Lucía, Justa, Ana María Láinez ["Anamama," "Viuda"] [aunt], Josefina Láinez ["Pepa," "Pepita," "Mamachica"] [aunt], Justita Láinez ["Tita," "Tina," "Vinagera"] [aunt], and Martha Láinez ["Nenatony"] [aunt].

Additional material consists of correspondence by Mujica Láinez to Alberto Manguel (1973-1984); a photograph of Mujica Láinez dedicated to Manguel (1971); and a copy of a typed manuscript by Jorge Luis Borges about Mujica Láinez, with holograph corrections by Mujica Láinez (1979).