The courtly lover existed to serve his lady. His love was invariably adulterous, marriage at that time being usually the result of business interest or the seal of a power alliance. Ultimately the lover saw himself as serving the all-powerful god of love and worshipping his lady-saint. Faithlessness was the mortal sin.

The philosophy found little precedent in other, older cultures. Conditions in the castle civilization of 11th-century southern France, however, were favourable to a change of attitude toward women. Castles themselves housed many men, few women; poets, wishing to idealize physical passion, looked beyond the marriage state. The Roman poet Ovid undoubtedly provided inspiration in the developing concept of courtly love. His Ars amatoria had pictured a lover as the slave of passion—sighing, trembling, growing pale and sleepless, even dying for love. The Ovidian lover's adoration was calculated to win sensual rewards; the courtly lover, however, while displaying the same outward signs of passion, was fired by respect for his lady. This idealistic outlook may be explained partly by contemporary religious devotions, both orthodox and heretical, especially regarding the Virgin Mary, and partly by France's exposure to Arab mystical philosophy (gained through contacts with Islām during the Crusades), which embodied concepts of love—as a delightful disease, as demanding of faithful service—that were to characterize courtly love.

Courtly love may therefore be regarded as the complex product of numerous factors—social, erotic, religious, and philosophical. The idea spread swiftly across Europe, and a decisive influence in this transmission was Eleanor of Aquitaine, wife first to Louis VII of France and then to Henry II of England, who inspired some of the best poetry of Bernard de Ventadour, among the last (12th century) and finest of troubadour poets. Her daughter Marie of Champagne encouraged the composition of Chrétien de Troyes's Lancelot (Le Chevalier de la charrette), a courtly romance whose hero obeys every imperious (and unreasonable) demand of the heroine. Soon afterward the doctrine was “codified” in a three-book treatise by André Le Chapelain (q.v.). In the 13th century a long allegorical poem, the Roman de la rose, expressed the concept of a lover suspended between happiness and despair.

Courtly love soon pervaded the literatures of Europe. The German minnesinger (q.v.) lyrics and court epics such as Gottfried von Strassburg's Tristan und Isolde (c. 1210) are evidence of its power. Italian poetry embodied the courtly ideals as early as the 12th century, and during the 14th century their essence was distilled in Francesco Petrarch's sonnets to Laura. But perhaps more significantly, Dante had earlier managed to fuse courtly love and mystical vision: his Beatrice was, in life, his earthly inspiration; in La divina commedia (Divine Comedy, The) she became his spiritual guide to the mysteries of Paradise. Courtly love was also a vital influential force on most medieval literature in England, but there it came to be adopted as part of the courtship ritual leading to marriage. This development, discussed in C.S. Lewis' Allegory of Love (rev. ed., 1951), became more pronounced in later romances.