Mariya-Cecilia Abramovna Mendelson-Prokofieva (Russian: Мария-Цецилия Абрамовна Мендельсон-Прокофьева), typically referred to as Mira Mendelson (Russian: Мира Александровна Мендельсон), (January 8, 1915 [O.S. December 26, 1914] – June 8, 1968) was a Russian poet, writer, and translator who was the second wife of the composer Sergei Prokofiev. She was the co-librettist of her husband's operas Betrothal in a Monastery, The Story of a Real Man, and War and Peace, as well as the ballet The Tale of the Stone Flower.

Mendelson was born in Kiev on January 8, 1915; the only child of Abram Solomonovich (1885–1968) and Vera Natanovna Mendelson (1886–1951). Her father was an economist and statistician, while her mother had earned recognition for her work as a member of the Communist Party of the Soviet Union. As a young woman she began her studies in higher education at the Energy Sector of the Genplan Institute of Moscow, before transferring to the Maxim Gorky Literature Institute to major in poetry and English translation.

The details of how she first met Prokofiev, or how her professional relationship with the then married composer developed into an extramarital affair remain unclear. According to Mendelson's memoirs, she met her future husband in August 1938 at a resort in Kislovodsk, where they were vacationing with their respective families. She remembered that the son of Alexander Fersman drew her attention to Prokofiev's presence at the resort. Shortly thereafter she saw the composer for the first time:

At lunchtime a diminutive woman entered the dining room of the sanatorium, followed by a tall man with an extraordinary stride and a very serious expression on his face. Maybe this is what they mean by 'love at first sight.'

In a letter written to Prokofiev less than a year before their final separation, his then wife Lina decried what she perceived as Mendelson's calculated pursuit of him:

Remember what you wrote after the first meeting. It was hardly you who chose [Mendelson and her family], but they who "chose" you—where? At a health resort—you, not some speck of sand, but [Sergei Sergeyevich Prokofiev], the leading composer of the nation, a famous person with a family man aura, twice as old. Perhaps you will say "love at first sight"—who will believe that? There were sufficient witnesses in Kislovodsk to the fact that she followed you everywhere.

After their first conversation on August 26, Mendelson and Prokofiev began taking walks together wherein they discussed music and literature. Mendelson later wrote that she had been fascinated by Prokofiev's "foreign" elegance and charm. The composer maintained feeling a sense of déjà vu upon meeting her, citing her resemblance to his previous infatuations, Nina Meshcherskaya and Ida Rubinstein. At the end of their vacation they promised each other to meet again in Kislovodsk the following year and to remain in contact in the meantime. In January 1939 he gifted to her a signed photograph of himself, which bore the inscription: "To a blossoming poet, from a modest admirer." For his birthday in April of that same year, Mendelson wrote a poem for him where she declared that "your necklace of kisses, tender words is a gift/brighter than all the diamonds in the world."

Early on their relationship had raised the suspicions of Prokofiev’s first wife. She stated in interviews after her former husband's death that he had initially described Mendelson as "just some girl who wants me to read her bad poetry." Later he defended his meetings with her on professional grounds, telling his wife that Mendelson was helping him to find suitable libretti for his projected operas. By 1939, the relationship between composer and budding poet became a source of gossip in the Soviet musical world. Lina’s suspicions were confirmed in a message to her from an acquaintance, but felt powerless to impede her husband from continuing his affair. When he finally disclosed the affair to his wife, she replied that she would not object to it so long as he did not go to live with Mendelson.