How did Mozart influence Joseph Haydn’s later music?

The relationship between Joseph Haydn and Wolfgang Amadeus Mozart was one of mutual inspiration and deep friendship. Far from being set in his ways, the mature Haydn remained flexible and receptive to new ideas, and his later music reflects the significant impact of his younger friend.1

This influence is particularly evident in Haydn’s later symphonic and chamber works:

• Symphonic Development: Haydn’s late Paris Symphonies (1785–86) and London Symphonies (1791–95) reflect the influence of Mozart and represent the height of Haydn’s power. These works feature complex thematic development where each instrument shares in the melodic evolution, moving beyond earlier, simpler textures.2
• Chamber Music: During the period of their close contact (c. 1786–90), Haydn composed 18 string quartets (Opus 50, 54, 55, and 64) that are characterized by an increasing use of chromaticism to produce poignant, expressive effects.3

Ultimately, the two composers learned from one another; while Mozart famously credited Haydn with teaching him how to write string quartets, Haydn’s own artistry was enriched by the creative brilliance of his colleague.1