Leona Rostenberg was born in the Bronx, New York. In 1930, as a senior at New York University, she met Madeleine Stern, then a freshman at Barnard College. Ms. Rostenberg earned a master's degree at Columbia and then worked on her doctorate, but her thesis was rejected. (Years later, Columbia awarded her the PhD, based on the books she had written in the interim.) Ms. Rostenberg decided to apprentice herself to a rare book dealer. After a few years, she borrowed $1,000 from Ms. Stern to start her own rare book shop; eventually Ms. Stern quit her teaching job and became her business partner. The two friends lived first in Ms. Rostenberg's family house in the Bronx, and then in Manhattan, and traveled together to Europe and in the USA in search of rare books. In 1942, they were doing research together in the Houghton Library at Harvard after being tipped off by a scholar that Louisa May Alcott might have written some potboilers under a pseudonym. Their discovery of five letters and Alcott's pen name of A.M. Barnard caused a literary sensation and altered Alcott scholarship. It led to Ms. Stern's classic biography Louisa May Alcott (1950) and books that are still being published today. Leona Rostenberg wrote half a dozen books on her own, such as An Antiquarian's Credo (1976), and several more with Ms. Stern. Their 1997 joint autobiography, Old Books, Rare Friends: Two Literary Sleuths and Their Shared Passion, became a bestseller; it was folowed by Bookends: Two Women, One Enduring Friendship (2001). Ms. Rostenberg was elected president of the Antiquarian Booksellers Association of America in 1973, a rare honor for a woman in a mostly male profession.