Julianna Luisa Margulies (born June 8, 1966) is an American actress.

After several small television roles, Margulies achieved success in her continuing role as Nurse Carol Hathaway on the NBC medical drama ER, for which she won an Emmy Award. Since her departure from ER in 2000, Margulies has appeared sporadically in film and television, and has also worked in theater.

Margulies, the youngest of three daughters, was born in Spring Valley, New York, the daughter of Francesca, a ballet dancer and eurythmy teacher, and Paul Margulies, a writer who wrote the Alka-Seltzer catch phrase "Plop, Plop, Fizz, Fizz, oh what a relief it is". Margulies attended grade school at Green Meadow Waldorf School and high school at High Mowing School. As a child, she lived in New York, France, and England. Margulies's parents are Jewish, descended from immigrants from Austria, Hungary, and Romania; her mother converted to Christianity when Julianna was five years old.