By 1721, Bach's third year as court organist at Anhalt-Cothen, he was becoming restless and began looking for career opportunities outside the small town. In March, he assembled these 6 concerti and presented them, by way of a job application, to the Margrave of Brandenburg. The concerti have little in common; the dedication page Bach wrote for the collection merely indicates that they are six pieces for several instruments. Indeed, the six works attempt to use as many different combinations of common instruments as the composer could think of.
The First Concerto in F major calls for two French horns, three oboes, bassoon, and violine piccolo[?] as well as two violins, viola, and basso continuo for accompaniment. This varied group of instrumentalists presents a dance-like concert. An earlier version of this concerto survives as a sinfonia[?], BWV 1046a.
The Second Concerto, also in F major, calls for a somewhat simpler ensemble of trumpet, recorder, oboe, and violin, with two violins, viola, and basso continuo again accompanying.
The Third Concerto in G major is often cited as the prototype of the modern string quartet as Bach here calls for only string instruments. The three violins, three violas, and three cellos are accompanied by basso continuo. The dazzling third movement shows up in many movie and commercial soundtracks.
The Fourth Concerto in G major for violin and two flutes accompanied by two violins, viola, and basso continuo uses these common instruments in uncommon ways; the solo violin part actually mimicks the continuo accompaniment at times, moving what is traditionally foundation to the treble register.
The Fifth Concerto in D major for flute, violin, and harpsichord with violin, viola, and basso continuo support makes use of a very popular chamber music ensemble (flute, violin, and harpsichord). Bach, himself a keyboard virtuoso, included a stunning harpsichord cadenza in this concerto, prefiguring the piano concerti of Mozart and Beethoven.
The Sixth Concerto in B-flat major sets two trio groups against each other. One the one side sit the "modern" violas (two) and cello while on the other side of the stage sit the "old-fashioned" violas da gamba and double bass. These opposed low-register trios present a series of call-and-response motifs that is totally without precedent in the musical literature.