Bach's 15 Sinfonias (aka 3 part inventions) were written for solo keyboard. This transcription has the top voice pulled out for a treble instrument like a flute or violin (oboe, clarinet, etc). The lower 2 voices are transcribed for a piano. So these pieces become available to be played by a flutist (violinist, etc.) accompanied by piano.They are great for study, performance as encores, or as concert pieces.