Felix Mendelssohn wrote six numbered string quartets which were published during his lifetime:
Mendelssohn also wrote another quartet in E-flat major at the age of 14, just after he had composed his 13 string symphonies. However, the quartet was never published in his lifetime and so was never assigned an opus number.
Mendelssohn's first two numbered quartets were published out of order, whilst his next three quartets were published together as Op. 44 and were all dedicated to Crown Prince Gustavus of Sweden.
Mendelssohn's final string quartet was composed after the death of his sister, which was a devastating blow to Mendelssohn. The quartet was also his last major work, as he died only two months after its completion. The piece was published shortly before his death along with a set of four pieces for string quartet also composed in his final years.