In the play's final scene, Romeo finds Juliet's seemingly "dead" body and, rather than face life without her, he swallows a vial of poison moments before Juliet wakes up. When Juliet realizes her husband is dead, she tries to kill herself by kissing Romeo. Since there's not enough poison left on his lips, she stabs herself with Romeo's "happy dagger" (5.3.3).
As tragic as it is, the ending of Romeo and Juliet shouldn't surprise anyone. We're told from the get-go that our "star-crossed lovers [will] take their life" (Prologue). We also know that Romeo and Juliet belongs to the genre of "tragedy," and Shakespeare's tragedies always, always, always end in death. (You can read more about this by going to "Genre," but then come right back, or else.)
In the Prologue, the Chorus also tells us that "their death [will] bury their parents' strife," and it does. In one of the most ironic moments of the play, the couple's parents are so devastated by the deaths of their children that they kiss and make up, each father promising to erect an elaborate statue to commemorate the other's child (5.3.3). Hmm. Do we detect a bit of competition here? When Montague announces his plans to "raise [Juliet's] statue in pure gold," he basically tells Capulet he's going to outdo him. "But I can give thee more," he brags (5.3.3). Of course, if Montague and Capulet had put an end to the long-standing family feud earlier, Romeo and Juliet would still be alive, which is why the prince calls the parents' reconciliation a "glooming peace" (5.3.11).
Shakespeare scholar Marjorie Garber offers some interesting insight about the specific way that Romeo and Juliet end their lives. Romeo drinks poison from a "cup," a traditional symbol of female sexuality. (This same symbolism is used in the Da Vinci Code, where the Grail, a big V-shaped goblet, represents the eternal feminine.) Juliet, in contrast, stabs herself with Romeo's dagger – a traditional image of male sexuality. Garber argues that, symbolically, Romeo and Juliet combine physical death and sexual climax.
The way Romeo's and Juliet's deaths resemble acts of sexual fulfillment doesn't really surprise us. Death and sex are linked throughout the entire play (which you can read more about in "Symbols") and Juliet does say that ingesting poison by kissing Romeo's lips would "make [her] die with a restorative" (5.3.2). In other words, she's suggesting that the kiss and the poison would heal or "restore" her by reuniting her with her husband. But, since poison isn't a viable option for her, she chooses to unsheathe Romeo's sword and then thrusts it into her own body.
After you read the ending of Shakespeare's play, we recommend watching the following film clips: 1) The ending of Franco Zeffirelli's 1968 film version of the play and 2) the final scene in Baz Luhrmann's 1996 film adaptation, Romeo + Juliet.