Gail Sheehy, a journalist who plumbed the interior lives of public figures for clues to their behavior, examined societal trends as signposts of cultural shifts and, most famously, illuminated life changes in her book “Passages,” died on Monday August 24 2020 at a hospital in Southampton, N.Y. She was 83. Her daughter, Maura Sheehy, said the cause was complications of pneumonia. Gail Sheehy a lively participant in New York’s literary scene and a practitioner of creative nonfiction, studied anthropology with Margaret Mead. She was a star writer at New York and later married its co-founder, Clay Felker, who encouraged her to write “big” stories. Ms. Sheehy’s 1976 book was a New York Times best-seller for more than three years. The Library of Congress ranked it as one of the 10 most influential books of modern times. Gail Merritt Henion was born on Nov. 27, 1936, in Mamaroneck, N.Y., and grew up there, attending its public schools. Her mother, Lillian Rainey Henion, was a homemaker. Her father, Harold Henion, owned an advertising business. Ms. Sheehy graduated from the University of Vermont in 1958 with a bachelor’s degree in English and home economics. Her first job was as a consumer representative for J.C. Penney. She married Albert F. Sheehy in 1960 and moved to Rochester, N.Y., where he attended medical school and she worked as a fashion coordinator at McCurdy’s department store, decorating windows. She then interviewed for a job on the fashion page at The Rochester Democrat and Chronicle, though the editor was reluctant to hire her. The couple soon moved back to New York City — they would divorce in the late 1960s — and she landed a job at The New York Herald Tribune. Ms. Sheehy and Clay Felker had a tempestuous, passionate, on-again-off-again romance that, after many years, turned into a stable relationship and, in 1984, into a happy marriage. They raised Maura Sheehy, from Ms. Sheehy’s first marriage, and adopted a Cambodian refugee, Mohm Sheehy, who had lost most of her family during the murderous Pol Pot regime. In addition to her daughters, Ms. Sheehy is survived by her sister, Patrica Klein; her companion, Robert Emmett Ginna Jr., a former Harvard professor and a co-founder of People magazine; and three grandchildren.