This dissertation examines the culture of adolescent girlhood and identity performance as they coexist with social networking. Through application of adolescent development theory, identity performance theory, and girls' studies, the dissertation answers the question, "How do adolescent girls perform identity to their peers both in everyday life and using social networking sites like MySpace.com?" By incorporating participant observation, textual analysis and guided conversation interviews, I explore the culture of girlhood at an all-girls' high school, and the performance of identity, adolescence, and gender of twenty-two participants. This dissertation differs from the previous literature on adolescent girls' identity performances on social networking sites by including the actual voices of the girls. I allow the girls to talk about the way they present themselves both to friends and family as well as through their social networking "MySpace.com" pages. Grounded in theory, I expand the developmental theories of Erikson (1985), Bronfenbrenner (1979) and Elkind (1981, 2001) by demonstrating the need for an addition to the ecological systems of development with a "cybersystem" as well as explore Elkind's "imagined audience" and argue that this "imagined audience" has been "actualized" through social networking. Identity performance, as delineated by Goffman (1959), is used to discuss the ways in which both the changing and overlapping social contexts of teenage girls requires a constant readjustment of performing self, a fluid identity practice. Finally, using the emerging field of girls' studies this work is informed by the feminist work of Gilligan (1982) and McRobbie's (1982, 1991, 2000) who understood the importance of foregrounding the culture of adolescent girls. Overall, this dissertation recognizes the changing social environment for teens as they move into adulthood and looks to acknowledge the increasing struggle for performing identity in girls' everyday lives.