Barney practiced, and advocated, non-monogamy. As early as 1901, in Cinq Petits Dialogues Grecs, she argued in favor of multiple relationships and against jealousy.
She once wrote out a list, divided into three categories: liaisons, demi-liaisons, and adventures. The artist and furniture designer Eyre de Lanux, with whom she had an off-and-on affair for several years, was listed as an adventure.
Lanux is best known as having been one of the many long-term lesbian lovers of writer and artist Natalie Barney. The two met through common friends, at Barney's popular Paris Salon and became an on-again-off-again couple for many years.
Due in part to Jean Chalon's early biography of Barney, published in English as Portrait of a Seductress: The World of Natalie Barney, she has become more widely known for her many relationships than for her writing or her salon.