The Overture in E major, Op. 21, was written by Mendelssohn at 17 years and 6 months old (it was finished on 6 August 1826), and George Grove called it "the greatest marvel of early maturity that the world has ever seen in music". It was written as a concert overture, not associated with any performance of the play. The Overture was written after Mendelssohn had read a German translation of the play in 1826. The translation was by August Wilhelm Schlegel, with help from Ludwig Tieck. There was a family connection as well: Schlegel's brother Friedrich married Felix Mendelssohn's aunt Dorothea.
While a romantic piece in atmosphere, the Overture incorporates many classical elements, being cast in sonata form and shaped by regular phrasings and harmonic transitions. The piece is also noted for its striking instrumental effects, such as the emulation of scampering 'fairy feet' at the beginning and the braying of Bottom as an ass (effects which were influenced by the aesthetic ideas and suggestions of Mendelssohn's friend at the time, Adolf Bernhard Marx). Heinrich Eduard Jacob, in his biography of the composer, said that Mendelssohn had scribbled the chords after hearing an evening breeze rustle the leaves in the garden of the family's home.
The Overture is cast in E major, a key especially genial for the stringed instruments of the orchestra. Following the first theme in the parallel relative minor (E minor) representing the dancing fairies, a transition (the royal music of the court of Athens) leads to a second theme, that of the lovers. A final group of themes, suggesting the craftsmen and hunting calls, closes the exposition. The fairies dominate most of thedevelopment section and ultimately have the final word in the coda, just as in Shakespeare's play.
The Overture was premiered in Stettin (then in Prussia; now Szczecin, Poland) on 20 February 1827, at a concert conducted by Carl Loewe. Mendelssohn had turned 18 just over two weeks earlier. He had to travel 80 miles through a raging snowstorm to get to the concert, which was his first public appearance. Loewe and Mendelssohn also appeared as soloists in Mendelssohn's Concerto in A-flat major for 2 pianos and orchestra, and Mendelssohn alone was the soloist for Carl Maria von Weber's Konzertstück in F minor. After the intermission, he joined the first violins for a performance of Beethoven's Ninth Symphony.
The first British performance of the Overture was conducted by Mendelssohn himself, on 24 June 1829, at the Argyll Rooms in London, at a concert in benefit of the victims of the floods in Silesia, and played by an orchestra that had been assembled by Mendelssohn's friend Sir George Smart.