Ludwig van Beethoven's opus 18, published in 1801 by T. Mollo et Comp in Vienna, consisted of his first six string quartets. They were composed between 1798 and 1800 to fulfill a commission for Prince Lobkowitz, who was the employer of Beethoven's friend, the violinist Karl Amenda. They are thought to demonstrate his total mastery of the classical string quartet as developed by Haydn and Mozart. The order of publication (numbering within the opus) does not correspond to the order of composition. Beethoven composed these quartets in the sequence 3, 1, 2, 5, 6, 4.
* String Quartet No. 1 in F major
* String Quartet No. 2 in G major
* String Quartet No. 3 in D major
* String Quartet No. 4 in C minor
* String Quartet No. 5 in A major
* String Quartet No. 6 in B♭ major