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. Her more notable roles include Morgaine in the 2001 miniseries The Mists of Avalon and the voice of the female iguanadon Neera in the animated film Dinosaur (2000).

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 were Jewish, descended from immigrants from Austria, Hungary, and Romania.