Am I the only one who had no idea?
From Wikipedia:
In an interview with the Jewish Telegraph, Kauffman confirmed that Rachel is Jewish. On the character's "Jewish ties", Kauffman told j. that Rachel had always been Jewish "in our minds", explaining, "You can’t create a character with the name 'Rachel Green' and not from the get-go make some character choices". Prior to this, critics and fans had long speculated whether or not Rachel is Jewish; there are entire websites entirely devoted to discussing this. Vulture's Lindsey Weber, who identifies herself as Jewish, observed several similarities and Jewish stereotypes she shares with the character, citing the facts that Rachel refers to her grandmother Ida Green as "Bubbe", Long Island origin, and engagement to a Jewish doctor as allusions to the character's Jewish culture. In her book Changed for Good: A Feminist History of the Broadway Musical, author Stacy Wolf identified Rachel as one of several popular female television characters who embodied Jewish stereotypes during the 1990s and often served as "the butt of the shows' jokes." Meanwhile, JDate's Rebecca Frankel cited Rachel as one of the earliest and most prominent examples of the Jewish American Princess stereotype on screen. Writing for the University of North Carolina at Chapel Hill, Alicia R. Korenman also acknowledged Rachel's initial Jewish American Princess qualities, describing her as "spoiled, dependent on her father's money and her fiance's, is horrified at the thought of working for a living and generally inept in her attempts to do so, and is eventually revealed to have had a nose job", which she eventually overcomes as they become less "evident in later seasons of the show". In his article "Princesses, Schlemiels, Punishers and Overbearing Mothers", Evan Cooper described Rachel as a "de-semitized" Jew because, aside from her name, "there is never any discussion of experiences of growing up in a Jewish culture, no use of Yiddish, and few, if any, references to family members with distinctively Jewish surnames". Cooper continued to write that although Rachel possesses some Jewish American Princess traits, she is more similar to the "little woman" stereotype. The New York Post's Robert Rorke labeled Rachel "a rehabilitated Jewish American Princess", in contrast to her sister Amy (Christina Applegate) who remains "selfish, condescending and narcissistic."