This text investigates the historical origins and structural composition of Joseph Haydn's Missa brevis Sancti Joannis de Deo, commonly known as the 'Little Organ Mass'. The editors provide a critical analysis of the work's provenance, tracing its 1775 commission for the Brothers of Mercy in Eisenstadt and examining the collaborative elements involving Michael Haydn. The volume serves as a scholarly resource for performers and musicologists, detailing the specific instrumentation and editorial decisions required for accurate performance.

Musicologists and choral directors frequently cite this edition as a standard reference for the 'Little Organ Mass' due to its inclusion of critical commentary and source verification. Experts highlight the clarity of the editorial notes, which effectively distinguish between the contributions of the Haydn brothers for modern performers.