Six works belong to opus 9 – the first group of Haydn’s string quartets of which we know. The composer also went new ways as far as form was concerned: whereas he had still adhered to the five movement divertimento in the previous quartets opus 1 and 2, in this case he favoured four movements, something he continued in the future. Apart from this, he also expanded the register and experimented with metric surprises (for instance in the trio of the minuet from the G major quartet).

• Quartet C major op. 9,1 Hob. III:19
• Quartet E flat major op. 9,2 Hob. III:20
• Quartet G major op. 9,3 Hob. III:21
• Quartet d minor op. 9,4 Hob. III:22
• Quartet B flat major op. 9,5 Hob. III:23
• Quartet A major op. 9,6 Hob. III:24