Jakob Ludwig Felix Mendelssohn Bartholdy (3 February 1809 – 4 November 1847), widely known as Felix Mendelssohn, was a German composer, pianist, organist and conductor of the early Romantic period. Mendelssohn's compositions include symphonies, concertos, piano music, organ music and chamber music. His best-known works include the overture and incidental music for A Midsummer Night's Dream (which includes his "Wedding March"), the Italian and Scottish Symphonies, the oratorios St. Paul and Elijah, the Hebrides Overture, the mature Violin Concerto, the String Octet, and the melody used in the Christmas carol "Hark! The Herald Angels Sing". Mendelssohn's Songs Without Words are his most famous solo piano compositions.

Mendelssohn's grandfather was the Jewish philosopher Moses Mendelssohn, but Felix was initially raised without religion until he was baptised aged seven into the Reformed Christian church. He was recognised early as a musical prodigy, but his parents were cautious and did not seek to capitalise on his talent. His sister Fanny Mendelssohn received a similar musical education and was a talented composer and pianist in her own right; some of her early songs were published under her brother's name and her Easter Sonata was for a time mistakenly attributed to him after being lost and rediscovered in the 1970s.

Mendelssohn enjoyed early success in Germany, and revived interest in the music of Johann Sebastian Bach, notably with his performance of the St Matthew Passion in 1829. He became well received in his travels throughout Europe as a composer, conductor and soloist; his ten visits to Britain – during which many of his major works were premiered – form an important part of his adult career. His essentially conservative musical tastes set him apart from more adventurous musical contemporaries, such as Franz Liszt, Richard Wagner, Charles-Valentin Alkan and Hector Berlioz. The Leipzig Conservatory, which he founded, became a bastion of this anti-radical outlook.

After a long period of relative denigration due to changing musical tastes and antisemitism in the late 19th and early 20th centuries, his creative originality has been re-evaluated. He is now among the most popular composers of the Romantic era.

Felix Mendelssohn was born on 3 February 1809, in Hamburg, at the time an independent city-state, in the same house where, a year later, the dedicatee and first performer of his Violin Concerto, Ferdinand David, would be born. Mendelssohn's father, the banker Abraham Mendelssohn, was the son of the German Jewish philosopher Moses Mendelssohn, whose family was prominent in the German Jewish community. Until his baptism at age seven, Mendelssohn was brought up largely without religion. His mother, Lea Salomon, was a member of the Itzig family and a sister of Jakob Salomon Bartholdy. Mendelssohn was the second of four children; his older sister Fanny also displayed exceptional and precocious musical talent.

The family moved to Berlin in 1811, leaving Hamburg in disguise in fear of French reprisal for the Mendelssohn bank's role in breaking Napoleon's Continental System blockade. Abraham and Lea Mendelssohn sought to give their children – Fanny, Felix, Paul and Rebecka – the best education possible. Fanny became a pianist well known in Berlin musical circles as a composer; originally Abraham had thought that she, rather than Felix, would be the more musical. But it was not considered proper, by either Abraham or Felix, for a woman to pursue a career in music, so she remained an active but non-professional musician. Abraham was initially disinclined to allow Felix to follow a musical career until it became clear that he was seriously dedicated.

Mendelssohn grew up in an intellectual environment. Frequent visitors to the salon organised by his parents at their home in Berlin included artists, musicians and scientists, among them Wilhelm and Alexander von Humboldt, and the mathematician Peter Gustav Lejeune Dirichlet (whom Mendelssohn's sister Rebecka would later marry). The musician Sarah Rothenburg has written of the household that "Europe came to their living room".

Abraham Mendelssohn renounced the Jewish religion prior to Felix's birth and he and his wife decided against having Felix circumcised. Felix and his siblings were at first brought up without religious education; on 21 March 1816, they were baptized in a private ceremony in the family's Berlin apartment by the Reformed Protestant minister of the Jerusalem Church, at which time Felix was given the additional names Jakob Ludwig. Abraham and his wife Lea were baptised in 1822, and formally adopted the surname Mendelssohn Bartholdy (which they had used since 1812) for themselves and for their children.