Orlando complains that, though his eldest brother Oliver was charged in their father's will to care for him, he is mistreated by Oliver and lives as a low laborer rather than as the gentleman he is meant to be. Meeting his brother, Orlando locks him in a fighting hold until Oliver promises to give him the meager fortune promised by their father. Oliver, of course, has no intention of keeping his promise, as he soon reveals to the audience. Charles the wrestler comes to visit Oliver with news from the court: Duke Frederick has overthrown his older brother Duke Senior, who spends his exile in the Forest of Arden with his loyal followers. Charles mentions that he has heard a rumor that Orlando intends to challenge him in a wrestling match. Oliver encourages Charles to be merciless with his opponent in the upcoming encounter. At the Duke's palace, Duke Frederick's daughter Celia tries to cheer up her cousin Rosalind, daughter of the banished Duke Senior. Their conversation turns to the idea of falling in love. The wrestling match is announced, and they are delighted to see the handsome, young Orlando defy the odds and beat Charles. Rosalind, despite her earlier vow that she will not fall seriously in love, is smitten with Orlando. She tries to talk to the dumbstruck Orlando, and gives him her necklace as a token. No sooner are the girls gone than the lovesick Orlando is warned by LeBeau that he should flee the court: Duke Frederick is not pleased to have in his midst Orlando, the son of a dear friend of the exiled Duke. Duke Frederick's displeasure extends to Rosalind, whom he claims he has spared only for his daughter Celia's sake. When her father banishes Rosalind, Celia pledges that her cousin will not go alone: the two of them will run away together. They will disguise themselves for safety's sake—Celia as the fair "Aliena" and Rosalind as the page "Ganymede"—and will treat the journey as an adventure.
Duke Frederick discovers that the girls and the court jester, Touchstone, have left. He believes them to be in the company of Orlando, and orders his company to find the missing party. Though safe, by this time the travelers have arrived in Arden, and they are tired and hungry. In Arden they look on as two shepherds, Silvius and Corin, talk, the younger declaring himself more deeply in love than anyone who ever lived. The newcomers offer the older shepherd money for food and shelter. Arden proves a safer, though not always idyllic, place for the exiled Duke and his cohorts: in this remote setting they do not have to contend with the petty and often treacherous politics of the court. But Jaques makes a habit of dissenting from the general happiness: he condemns their hunting of innocent deer, revises the merry songs that the courtier Amiens sings, and wishes he could live the life of a Fool, free to criticize whatever and whomever he chooses. At his old servant Adam's suggestion, Orlando flees from his home, fearful of his brother's plot against him. Adam vows to follow Orlando faithfully, but is weakened by the journey. To procure much-needed food for Adam, Orlando tries to ambush Duke Senior's banquet, but his threats are ineffectual. The Duke turns to invite Orlando to share in their feast. When the Duke learns Orlando is the son of his old friend Rowland de Boys, he welcomes him and Adam heartily.
Duke Frederick orders Oliver to hunt down Orlando, but the faraway threat is not felt in Arden, where Rosalind, Celia, and Touchstone have found anonymous love poems—all addressed to Rosalind—tacked up on trees. The three laugh at the amateur poems until Celia reveals to Rosalind that the author of the poems is none other than Orlando. Rosalind's usually confident manner changes instantly. The news barely has time to register when Orlando himself appears. Still disguised as Ganymede, Rosalind greets Orlando. Orlando admits to Ganymede that he is the author of the posted poems and in love with Rosalind. Ganymede protests that Orlando does not act like one in love and challenges him to prove it. Ganymede devises a game which will either prove Orlando's love or "cure" it: Orlando will woo the page as if "he" were really his beloved Rosalind, and Ganymede, being generally difficult, will try to change his mind. After the encounter, Rosalind is uncertain whether Orlando's love is true. Orlando and the disguised Rosalind are not the only lovers in the forest. Touchstone plans to marry the dim-witted Audrey in order to legitimize their union, at least for as long as Touchstone is interested. And Rosalind, watching Silvius unsuccessfully court the disdainful Phebe, chastises the girl. But the attempt to help Silvius backfires: Ganymede becomes the object of Phebe's adoration.
When Orlando is late to meet Ganymede, "he" tells Orlando that a lover must never break a promise to his beloved. Quick to point out Orlando's misconceptions about love, Ganymede instructs Orlando that conversation should always come before a kiss. At the end of their encounter, Ganymede (as Rosalind) decides to give Orlando another chance to prove he can keep a promise. While waiting again for Orlando, Ganymede is greeted by Silvius, who has brought "him" a poem from Phebe. Phebe writes that she adores Ganymede even when he rejects her, and begs for his affection. Ganymede sends Silvius away, vowing to remedy the situation. At that moment Oliver, recently arrived in Arden, appears to explain Orlando's absence: Orlando's bonds of kinship proved greater than his desire for vengeance when he rescued his sleeping brother from a snake and a hungry lioness. Oliver displays a bloody handkerchief and Ganymede faints from the sight of the blood—but recovers in time to assure "his" new acquaintance that "he" was merely acting.
Act V and Epilogue
Touchstone meets William, a native of Arden who also desires Audrey's love and, though William is in no way a match for Touchstone, Touchstone warns William not to try to take Audrey away. In the meantime, Oliver and Celia have fallen in love, and Orlando gives his blessing to his brother's wedding plans. Rosalind gathers Orlando, Silvius, and Phebe together and extracts promises from them all: Orlando swears to cherish Rosalind, Silvius swears to cherish Phebe, and Phebe swears to accept Silvius as her husband if she should ever decide she does not want Ganymede. At Oliver's wedding, the god Hymen ushers in Celia and Rosalind, their true identities revealed. Duke Senior is ecstatic to find his daughter, as Orlando is to find his love, and Phebe, at last, is resigned to love Silvius. Orlando and Oliver's brother, Jaques de Boys, arrives at the wedding, bearing news. Duke Frederick, having set out for Arden to take care of his enemies, along the way met a religious man and has decided to live out the rest of his life under his guidance. Duke Senior's land is returned to him, and the exiles are free to return home to the court. Jaques alone opts not to return. He declares he will join Frederick and the religious man. And Rosalind leaves the audience with some parting wisdom.