101 in D major (Hoboken 1/101) is the ninth of the twelve London symphonies written by Joseph Haydn.

[1] On 3 March 1794, the work was premiered with an orchestra of 60 personally gathered by Haydn's colleague and friend Johann Peter Salomon, who also acted as concertmaster, in the Hanover Square Rooms, as part of a concert series featuring Haydn's work organized by Salomon; a second performance took place a week later.

The work is in standard four-movement form, as follows: The opening movement starts with a minor introduction consisting of 23 measures.

The secondary theme has a similar rhythmic pattern, also beginning with scales in the violins but descending this time, but it has more subtlety.

[10] Towards the middle of the movement, there is a dark, fierce passage in G minor, followed by Haydnesque humor and finally the clock theme once again.

Michael Steinberg said, "Haydn has a gratifying number of different clocks in his shop, offering 'tick-tock' in a happy variety of colors.

"[11] In 1793, Haydn had given his employer Prince Esterházy an elaborate musical clock, for which he wrote 12 short pieces, one of them being the basis for the third movement.