first it seems as though Romeo wants to hurry back to Verona to find out what happened to Juliet, or perhaps to avenge her death. It appears, however, that Romeo doesn't really care how Juliet died, only that she's dead. Immediately upon hearing the news, he's decided to die by her side.

It means he is defying fate—or attempting to, at any rate, because unfortunately fate will ultimately defeat both Romeo and Juliet.

Romeo has just been wrongly informed of Juliet's death. His immediate reaction to this tragic situation, as well as intense sorrow, is one of angry defiance. Romeo recognizes himself as the plaything of fortune and subject to the whims of fate. But he's not going to take this lying down; he's determined to take his fate into his own hands by heading back to Verona and killing himself in Juliet's tomb.

The irony here is that in his attempts to defy fate, Romeo is actually making it happen. For when Juliet wakes from her drug-induced slumbers and sees Romeo's dead body lying next to her, she stabs herself to death, thus fulfilling the sad fate of the star-cross'd lovers.

Before Romeo and his friends depart for the Capulets' party, Mercutio and Benvolio do their best to get him to go.  Romeo resists for a long time but finally gives in, saying,

My mind misgivesSome consequence yet hanging in the starsShall bitterly begin his fearful dateWith this night's revels, and expire the termOf a despised life closed in my breastBy some vile forfeit of untimely death. (1.4.107-112)

In other words, Romeo seems to have a premonition that the party that night will initiate a series of events that will end with his own early death. It's not a pleasant thought.  However, he still feels somewhat compelled to go by whoever "hath the steerage of [his] course" (1.4.113).  Thus, Romeo has a sense—even before he ever meets Juliet, let alone falls in love with her—that the party will begin the events that lead to his death, like a line of dominoes that cannot help falling down once the first one has been toppled.

Thus, when Balthasar tells Romeo that Juliet is dead, Romeo cries, "Is it e'en so? Then I defy you, stars!" He can hardly believe it, and his first instinct is to curse fate. I imagine him sort of shaking his fist at the sky. It's not that he is somehow going to move against fate, because he is about to go and enact what he imagined just a few nights ago.  Instead, the expression indicates his anger with fate and his curse of it.

"Is it e'en so? Then I defy you, stars!

In Act V scene I Romeo has just found out that Juliet is dead. He is beside himself with grief and he curses "I defy you, stars," which means he denies fate.  He denies fate's hold on him and he then plans to kill himself. He goes to buy poison and goes to Juliet's tomb. Later in Act V scene III Romeo again refers to the stars when he talks about the "inauspicious stars," referring again to fate, or as in this case, unlucky stars.  This is of course the beginning of the end for the "star crossed lovers."

The quote, “Then I defy you, stars,” was made after Romeo learned that Juliet was dead. By stars, he meant fate. There are multiple references to fate throughout the play. Earlier, Romeo and Juliet are referred to as “star-crossed lovers” and it is foreshadowed that they will take their own lives. After Romeo kills Tybalt in a fight he never wanted to have, he cries out, “O, I am fortune’s fool!” The quote about defying the stars is the third such obvious reference. In addition, there are numerous examples of fate standing between the lovers in Act 5 scene i-ii. There was no real reason that the friars plan should not have worked, and yet a series of missed opportunities causes the end that we know. With this quote, Romeo is declaring himself in opposition to destiny, although his resulting actions actually bring it about. Romeo commits suicide, prompting Juliet to do the same, which fulfills the tragic destiny of the star-crossed lovers.

This quote is actually set up in the Prologue, when the Chorus tells the audience that this play will focus on "A pair of star-crossed lovers" (Prologue, 6). Describing the lovers as "star-crossed" is another way of saying that an inescapable fate brings them together and, therefore, brings them to their tragic ends.

In act 5, scene 1, the readers hear this "star-crossed" idea come up again in Romeo's line,

Is it e’en so? Then I defy you, stars!

Romeo has learned of Juliet's "death" just before this line, and he believes himself to be defying destiny as he quickly decides to join his beloved in death:

Well, Juliet, I will lie with thee tonight.Let’s see for means. O mischief, thou art swiftTo enter in the thoughts of desperate men!

The dramatic irony is that, in making this choice, Romeo runs straight toward the destiny which the Chorus predicts in the Prologue—his own death—which then also prompts Juliet to kill herself as well.

Romeo's actual defiance of the "stars" would have been to live, but it seems that, in the end, he is incapable of escaping his destiny.

In literature, fate is often said to be “written in the stars,” implying that one cannot escape destiny. In Romeo and Juliet, when Romeo declares he will defy the stars, he is saying that he will defy fate and act on his own free will.When Romeo is told that Juliet has died, he believes his fate includes living a life without her. He rejects that notion and maintains that he will not allow his life to be ruled by fate, or “the stars.” For him, a life without Juliet was nothing less than a cruel fate. His decision to drink poison and take his own life is a defiant rejection of a destiny without Juliet.The phrase also refers to the beginning of the play, where Romeo and Juliet are described as "star-crossed lovers," which suggests that the stars were against them, and they would never be together. While the two worked tirelessly to thwart fate, in the end, they had no control over it. Ironically, Romeo’s bold decision to defy fate and “shake the yoke of inauspicious stars" is heartbreaking because it leads to the death of both of the young lovers.

The full quotation from Romeo and Juliet by William Shakespeare is:

Is it e'en so? Then I defy you, stars!

Thou know’st my lodging. Get me ink and paper,

And hire post horses. I will hence tonight.