Orlando, the youngest son of the now deceased Sir Roland de Boys, complains to Adam, the old family retainer, that his eldest brother, Oliver, has kept his Inheritance from him — that is, Oliver has neglected training Orlando to be a proper gentleman. Oliver arrives on the scene, and a bitter quarrel takes place. Adam parts the fighting brothers, and Oliver coldly promises to give Orlando his due. Learning that Orlando intends to challenge Duke Frederick's champion wrestler, a brute of a man called Charles, Oliver makes plans to have his brother killed in the ring. He convinces the slow-witted Charles that Orlando is plotting against him and that Orlando should be killed.
At the match the next day, Duke Frederick, his daughter Celia, and his niece, Rosalind, watch Charles and Orlando wrestle. Charles has seriously injured his first three opponents, but in the match with Orlando, the young man's great speed and agility defeat the duke's champion. At first, Frederick is very cordial to Orlando, but when he learns the youth's identity, he becomes furious and leaves. The reason for the duke’s leaving is that Orlando's dead father, Sir Roland de Boys, had at one time been Frederick's bitter enemy.
After Frederick stalks out, Celia and Rosalind congratulate Orlando, and Rosalind makes it clear that she finds him most attractive. Orlando returns her feelings, but he is so tongue-tied with embarrassment that he can say nothing.
At the ducal palace, we discover that Celia and her cousin Rosalind are as close as sisters; Rosalind is the daughter of the rightful duke, Duke Senior, whose throne has been usurped by his brother, Frederick. Frederick has banished Duke Senior, along with a band of his faithful followers, to the Forest of Arden to live the life of simple foresters. Until now, it is only the strong bond between Rosalind and Celia that prevents Duke Frederick from sending Rosalind away to share her father's exile. But suddenly, Frederick storms into the palace, accuses Rosalind of plotting against him, and, despite Celia's pleas for her cousin, banishes Rosalind. After her father leaves, Celia decides to go into exile with her cousin, and the girls set out for the Forest of Arden — Rosalind disguised as a young man, "Ganymede," and Celia disguised as a young country lass, "Aliena." Touchstone, Frederick's jester, accompanies them.
Meanwhile, Orlando returns home and is warned by the faithful Adam that Oliver is plotting to kill him. Together, they too decide to set out for the Forest of Arden, hoping that they will find safety there.
When his daughter Celia is missed, Frederick sends his men out to find Orlando. When he is informed of Orlando's flight to the Forest of Arden, Frederick assumes that Orlando is responsible for Celia's disappearance, and in a rage he sends for Oliver and commands him to find Orlando or else forfeit his entire estate to Frederick.
In the forest, Orlando and Adam join Rosalind's exiled father and his men, while Rosalind and Celia, still in disguise, purchase a little cottage and a small herd of sheep and settle down to a peaceful, pastoral existence. One day, however, Rosalind finds that the trees in the forest are all covered with sheets of poetry, dedicated to her. The author of these poems, of course, is Orlando. So, still pretending to be the young man Ganymede, Rosalind meets Orlando, who is in the throes of love-sickness for having apparently lost Rosalind. Ganymede offers to cure Orlando of his love-sickness by pretending to be his lady-love, Rosalind. Orlando, she says, should woo Ganymede as though "he" were Rosalind. In turn, Ganymede will do "his best" to act as moody and capricious as a girl might just do and, eventually, Orlando will weary of all the coy teasing and forget all about love — and Rosalind. Orlando agrees to try the plan.
Rosalind, meanwhile, continues to assume the guise of Ganymede and becomes accidentally involved in yet another complication: Silvius, a young shepherd, falls in love with Phebe, a hard-hearted shepherdess, but Phebe rejects Silvius' attentions and falls in love with the young, good-looking Ganymede.
In the midst of all this confusion, Oliver arrives in the Forest of Arden. He tells Ganymede of a near escape he has just had with death. His brother, Orlando, he says, saved him from being poisoned by a deadly snake as he slept, and later, Orlando killed a lioness that was ready to pounce on Oliver. Oliver then tells Ganymede that he has been sent to this part of the forest to seek out a young man known as Ganymede and tell him that Orlando cannot keep his appointment with him. And there is more news: while saving Oliver's life, Orlando was wounded. Hearing this, Ganymede swoons.
Later, in another part of the forest, Oliver and Celia meet and fall in love at first sight, and the jester, Touchstone, falls in love with a homely, simple-minded young woman named Audrey, who tends a herd of goats. Touchstone chases off Audrey's suitor, a lout named William, and although he realizes that he will never instill in Audrey any understanding of, or love for, such things as poetry, he still feels that he must have her.
Duke Frederick, meanwhile, is alarmed by the daily exodus of so many of the best men of his court to the alliance that is growing in the Forest of Arden; he therefore decides to journey to the forest himself and put a stop to all this business. At the forest's edge, however, he meets an old religious hermit and is miraculously converted.
At this point, Rosalind, still disguised as Ganymede, promises to solve the problems of everyone by magic. Shedding her male attire in private, she suddenly appears as herself, and the play comes to a swift close as she and Orlando, Oliver and Celia, Silvius and Phebe, and Touchstone and Audrey are married. Rosalind's father, the rightful duke, is joyous at finding his daughter again and is returned to his ducal status. Frederick's conversion is so complete that he renounces the world. At the end of the play, Rosalind comes forward and addresses the audience in a short but charming epilogue. In particular, she talks to all the lovers in the audience and wishes them well.