The story of Layla and Majnun is an old Arabic tale of ill-fated lovers, loosely connected with the life of a 7th century poet, Qays ibn Mulawwah. It has been told and retold many times over, and like all tales told and retold, the original story has acquired twists and permutations. The closest definitive version is that written by the 12th century Persian poet Nizami Ganjavi, who consolidated the many episodic tangents of the central love story into one poem. (English transliterations of the lovers' names include Leyli, Layli, Leyla, Mejnun, and Kais.)
One version of the story goes like this, in brief:
In the Arabian Desert an heir was born to a benevolent chieftain. The heir was named Qays, and he grew to be handsome, eloquent, and wise and much adored by his family and friends. In school one day, Qays fell in love with a new classmate, Layla. She was beautiful, and her most striking feature was her dark hair, for which she was named (Layla=night). Layla fell in love with Qays as deeply as he did with her. The two loved each other more or less quietly and chastely, but their passion did not go unnoticed, and they were teased by the other school children. Qays, ignoring the ridicule of his peers, spent his days gazing upon her and quietly chanting her name over and over. One day his passion for Layla overwhelmed him, and he burst out in class, repeatedly yelling her name. He fled the classroom and ran into the street, still yelling "Layla! Layla!" Thereafter he was called Majnun (madman).
Layla's family thought the love of Majnun disgraced their daughter. They took her away from the school where the two had met, and kept her sequestered in the family's tents in the desert. Layla and Majnun continued to love each other, and despaired at their forced separation. Majnun's parents pitied him, and so they asked Layla's father to give Layla to Majnun in marriage. Her proud father refused, claiming he would not give his daughter away to a madman who ran shamefully through the streets shouting her name. In response, Majnun flees into the wilderness, wandering through the desert and living in caves. He devotes himself to composing poems and songs in honor of Layla. His words of love are soon spread through the land, and he is both ridiculed and revered for his romantic devotion. The mad poet's family and friends make repeated attempts to persuade Layla's father to allow the lovers to be married and salvage the sanity of Majnun. Great battles are fought in the name of Majnun's love against Layla's tribe, but even in defeat her father refuses to give up his daughter. Majnun remains passive in these affairs, singing songs and reciting poems about Layla.
One day, Layla's father marries her to a wealthy nobleman. Layla remains steadfast in her devotion to Majnun, and refuses to consummate her marriage. Her husband is intelligent and kind and he permits her to retain her virginity; he, too, loves Layla and sadly accepts her love for Majnun. Eventually, Majnun learns of Layla's marriage, and he is thrown into even greater depths of despair. The two remain separate for the rest of their days, only occasionally seeing (but not speaking to or touching) each other. Sometimes they exchange letters. Majnun continues to sing songs about Layla, which continue to spread throughout Arabia, and her love for him never falters. Majnun befriends wild animals, which watch over him and accompany him as he walks through the desert. Majnun understands he will never enjoy Layla's love on earth, and waits for the joining of their souls in the afterlife. His only earthly happiness is the friendship of the animals.
Majnun's parents die. Layla's parents die, as does her husband. Layla, too, passes away. Majnun comes to her grave, where he laments unto death, his decaying body guarded by his animal-friends. One by one, the lovers and their loved ones wasted away; each dies heartbroken, bereft, and alone because the love of Majnun and Layla was denied.
It is a dark, sad story, like so many other great love stories. The tale is often compared to Romeo and Juliet (though in my opinion there are few similarities, aside from the fate of the lovers, and many great differences in form and content), though it's much older than Shakespeare's work. The story has nearly mythopoetic status in Arabic cultures. In addition to Nizami's edition and other poetic versions, the tale has been the inspiration for miniatures and other works of visual art, musical pieces, and an Azerbaijani opera.