Claude-Achille Debussy was a French composer. Along with Maurice Ravel, he was one of the most prominent figures associated with Impressionist music. He was made Chevalier of the Legion of Honour in his native France in 1903. Debussy was among the most influential composers of the late 19th and early 20th centuries. Debussy's music is noted for its sensory content and frequent usage of nontraditional tonalities. The prominent French literary style of his period was known as Symbolism, and this movement directly inspired Debussy both as a composer and as an active cultural participant.

Debussy was the oldest of five children. His father, Manuel-Achille Debussy, owned a china shop there; his mother, Victorine Manoury Debussy, was a seamstress. The family moved to Paris in 1867, but in 1870 Debussy's pregnant mother fled with Claude to his paternal aunt's home in Cannes to escape the Franco-Prussian War. Debussy began piano lessons there at the age of seven with an Italian violinist in his early 40s named Jean Cerutti; his aunt paid for his lessons. In 1871 he drew the attention of Marie Mauté de Fleurville, who claimed to have been a pupil of Frédéric Chopin. His talents soon became evident, and in 1872, at age ten, Debussy entered the Paris Conservatoire, where he spent the next 11 years. During his time there he studied composition with Ernest Guiraud, music history/theory with Louis-Albert Bourgault-Ducoudray, harmony with Émile Durand, piano with Antoine François Marmontel, organ with César Franck, and solfège with Albert Lavignac, as well as other significant figures of the era. He also became a lifelong friend of fellow student and distinguished pianist Isidor Philipp. After Debussy's death, many pianists sought Philipp's advice on playing Debussy's works.

During the summers of 1880, 1881, and 1882, Debussy accompanied Nadezhda von Meck, the wealthy patroness of Pyotr Ilyich Tchaikovsky, as she travelled with her family in Europe. The young composer's many musical activities during these vacations included playing four-hand pieces with von Meck at the piano, giving music lessons to her children, and performing in private concerts with some of her musician friends. A greater influence was Debussy's close friendship with Marie-Blanche Vasnier, a singer he met when he began working as an accompanist to earn some money, embarking on an eight-year affair together. She and her husband, Parisian civil servant Henri, gave Debussy emotional and professional support. Henri Vasnier introduced him to the writings of influential French writers of the time, which gave rise to his first songs, settings of poems by Paul Verlaine (the son-in-law of his former teacher Mme. Mauté de Fleurville).

As the winner of the 1884 Prix de Rome with his composition L'enfant prodigue, Debussy received a scholarship to the Académie des Beaux-Arts, which included a four-year residence at the Villa Medici, the French Academy in Rome, to further his studies (1885–1887). Debussy composed four pieces that were sent to the Academy: the symphonic ode Zuleima (based on a text by Heinrich Heine); the orchestral piece Printemps; the cantata La damoiselle élue (1887–1888) and the Fantaisie for piano and orchestra, which was heavily based on César Franck's music and therefore eventually withdrawn by Debussy. 

During his visits to Bayreuth in 1888–9, Debussy was exposed to Wagnerian opera, which would have a lasting impact on his work. Wagner's influence is evident in La damoiselle élue and the 1889 piece Cinq poèmes de Charles Baudelaire. Other songs of the period, notably the settings of Verlaine – Ariettes oubliées, Trois mélodies, and Fêtes galantes – are all in a more capricious style.

Around this time, Debussy met Erik Satie, who proved a kindred spirit in his experimental approach to composition and to naming his pieces. Both musicians were bohemians during this period, enjoying the same cafe society and struggling to stay afloat financially.

Debussy's private life was often turbulent. At the age of 18 he began an eight-year affair with Marie-Blanche Vasnier, the wife of Parisian civil servant Henri. The relationship eventually faltered following his winning of the Prix de Rome in 1884 and obligatory residence in Rome.

On his permanent return to Paris and his parents' home on the rue de Berlin he began a tempestuous relationship with Gabrielle ('Gaby') Dupont, a tailor's daughter from Lisieux, soon cohabiting with her on the rue de Londres, and later the rue Gustave Doré. During this time he also had an affair with the singer Thérèse Roger, to whom he was briefly engaged. Such cavalier behaviour was widely condemned, and precipitated the end of his long friendship with Ernest Chausson.

He ultimately left Dupont for her friend Rosalie ('Lilly') Texier, a fashion model whom he married in 1899. In 1904 Debussy was introduced to Emma Bardac, wife of Parisian banker Sigismond Bardac, by her son Raoul, who was one of his students. In contrast to Texier, Bardac was a sophisticate, a brilliant conversationalist, and an accomplished singer. After dispatching Lilly to her father's home at Bichain in Villeneuve-la-Guyard, Debussy secretly took Bardac to Jersey for a holiday. On their return to France, Debussy wrote to Texier on 11 August from Dieppe, informing her that their marriage was over, but still making no mention of Bardac. Debussy briefly moved to an apartment at 10 avenue Alphand. On 14 October, five days before their fifth wedding anniversary, Texier attempted suicide, shooting herself in the chest with a revolver while standing in the Place de la Concorde; she survived, although the bullet remained lodged in her vertebrae for the rest of her life. The ensuing scandal was to alienate Debussy from many of his friends, whilst Bardac was disowned by her family.

In the spring of 1905, finding the hostility towards them intolerable, Debussy and Bardac (now pregnant) fled to England, via Jersey. Bardac's divorce was finalized in May. After a brief visit to London, the couple returned to Paris in September. Their daughter (the composer's only child) Claude-Emma was born there on 30 October. Her parents were eventually married in 1908, their troubled union enduring until Debussy's death in 1918.