The Divertimento was the third Bartók work commissioned by Paul Sacher (1906-1999), the conductor of the Basel Chamber Orchestra who was also one of the greatest arts patrons of the 20th century. After the success of Music for Strings, Percussion and Celesta and the Sonata for Two Pianos and Percussion, Sacher requested a work for string orchestra. He arranged for the composer to spend a month in a small country house at Saanen in the Swiss Alps. The time was August 1939, that fragile historic moment in Europe when peace was still intact but was increasingly threatened by the spectre of war.

Bartók had long seen the handwriting on the wall. For some time, he had been contemplating emigration from Hungary; he was, however, reluctant to leave his aging mother behind. (After her death in December 1939, Bartók and his wife decided to emigrate to the United States.)

Bartók's goal in Divertimento was to write a piece that was easier to play than his earlier Basel commissions; the idea of alternation between orchestral soloists and entire sections (derived from the Baroque concerto grosso) was also part of his plan from the start. The title, which means “entertainment” in Italian, denotes an 18th-century musical genre prominent in the works of Mozart and his contemporaries.

As the late György Kroó, the leading Hungarian music critic of the last forty years, wrote in one of his books on Bartók: The title [Divertimento] alludes to the mood of the two Allegro movements, but it also expresses the transient “intermezzo” character of Bartók's three-and-a-half-week stay in Saanen amidst the tragic events of the era. The slow movement….is a premonition of the tragedy to come….

The first movement opens with a graceful, yet energetic theme, consisting almost entirely of melodic ornaments around a central note. The second theme, in sweet parallel thirds, is introduced by the solo string quartet.  Soon, however, the lyrical melodies run into what Kroó aptly characterized as a “stone wall” – extremely loud repeated notes, played in several octaves in a striking rhythmic pattern. Much of the movement revolves around this conflict between the lighthearted divertimento style and its harsh interruptions. The movement, which follows classical sonata form, ends with a Tranquillo (calm) closing section, proposing an idyllic solution to the conflict. In this coda, some of the earlier themes reappear in inversion (a technique dear to Bartók, which involves the substitution of ascending intervals for descending ones and vice versa).

The second-movement “Adagio” reopens and intensifies the struggle. It is stylistically related to the third movement of Music for Strings, with which it shares a tortuous, chromatic melodic style, and a progression from sadness to dramatic outburst. In Divertimento, the outburst, which is much more violent than the one in the earlier work, takes the form of a menacing two-note motif, first appearing at the end of a poignant Hungarian melody. In the course of the movement, the elegiac melodies are repeatedly interrupted by this motif, the last time at the very end, just when it seems that the music has finally reached a point of repose.
In the last movement, Bartók finally lets his hair down and treats us to some of the most cheerful moments in his entire output. The rhythmic and melodic elements of Hungarian folk dance are combined with Baroque procedures such as alternation between concertino and ripieno (the smaller and larger instrumental groups of the concerto grosso), and a fair amount of contrapuntal writing. A touch of delicious humor is provided by the pizzicato (plucked) passage shortly before the end.