Who is Rosaline Capulet?

Roseline never actually appears on stage in Romeo and Juliet. She is the woman who Romeo is infatuated with at the beginning of the play, and, in a way, she is the reason Romeo and Juliet meet. Romeo goes in disguise to the Capulet's party in hopes of seeing Roseline, but instead sees the beautiful Juliet. He immediately falls in love with her, and Roseline is forgotten. Although Roseline is not described in detail, we do know that she is said to be extremely beautiful, and has taken a vow a chastity till marriage, (and therefore will not return Romeo's affections.)