Romeo and Juliet meet at the ball held by Lord Capulet at his home. Because both of them are wearing masks, they do not know that they are from rival families. Romeo sees her from across the room and is immediately smitten:
O, she doth teach the torches to burn bright!
It seems she hangs upon the cheek of night
Like a rich jewel in an Ethiop's ear—
Beauty too rich for use, for earth too dear!
...Did my heart love till now? Forswear it, sight!
For I ne'er saw true beauty till this night.
Later, Romeo approaches her, and the two kiss twice. By this point, Juliet is as smitten as Romeo. It is at this point that Romeo discovers (by way of the Nurse) that Juliet is a Capulet. Later, the Nurse informs Juliet that Romeo is a Montague, and Juliet exclaims:
My only love, sprung from my only hate!
Too early seen unknown, and known too late!
Prodigious birth of love it is to me
That I must love a loathed enemy.
By this point, we realize that the two have experienced love at first sight, and this sets the rest of the play in motion. By the next scene, Romeo has met Juliet at her window and the two have agreed to get married. We can also wonder if the two lovers are not fated to meet, as Tybalt, recognizing Romeo, wants to confront him at the party. Capulet orders him not to, thus making it possible for Romeo and Juliet to meet.