As a young composer, Barber found his mature style quite quickly. Important works date from his student years at the Curtis Institute in Philadelphia, and his compositional approach did not change very much throughout his life. In 1935, his String Quartet was given its first performance in Rome, where it came to the attention of Toscanini. Encouraged by the favorable reception, Barber arranged the second movement for string orchestra, and it is this transcription that has since been known as the Adagio for Strings. Toscanini conducted the first performance of the Adagio with the NBC Symphony Orchestra in 1938.
The Adagio remained Barber's most popular composition throughout his life, and it is one of the best-loved American works in the literature. The long, lyrical lines suggest chant, and a vaguely modal tint helps to evoke a pious atmosphere in an earlier time. The structure of the work is also simple, with the same melodic idea presented originally in the first violins, then the violas, and then the cellos, with only minimal modifications. The cello statement grows to the piece's climax, a shimmering wave of sound that brings the listener to the entrance of heaven. The brief coda that follows is less optimistic, echoing the beginning and ending peacefully, but without genuine resolution. The work is regarded as the outstanding example of 20th-century lyricism in the string orchestra medium: newer works, if they evoke a similar mood, can receive no higher praise than to be described as "like the Barber Adagio."