Romeo and his friends arrive at the party, and Romeo, immediately forgetting about Rosaline, sees Juliet, and falls instantly in love with her.  Tybalt sees Romeo there, and wants to attack him, but Lord Capulet says no.  Romeo meets with Juliet, who falls in love with him, also, and they both find out from the nurse, Juliet's servant, that they are from the opposite of the two fighting families.  Romeo and Juliet do not care, though, because they are already in love.