Bach’s Trio Sonatas for the organ were penned after 1723, a time when he dedicated himself to instrumental music, in part to teach his children and improve the flexibility of their fingers (I’ll say!). The are ‘trio’ since there are three voices, all inter-related and interweave harmonically, works of his baroque genius, and can be played on the organ – two keyboards and pedals – or with other instruments (flute, violin, harpsichord). For a fuller treatment of the history and theory, please see here.
And for a taste of the trios to tantalize, here is the Bach Netherlands Society, as played by Wolfgang Zerer: