Czerny gained fame as an interpreter of Beethoven's piano works. In 1816 he started a weekly series of concerts at his home, devoted solely to Beethoven's music. Czerny wrote commentaries on the performance of Beethoven's piano music. These are an extraordinarily valuable and authoritative source for all pianists. He started teaching at age 15. His two most famous pupils were Sigismund Thalberg and Franz Liszt. Despite teaching at times as many as ten hours a day, he managed to compose an immense amount of music, over 1,000 works. He composed so prolifically that he set up a series of desks in his workroom. Each would hold a composition in the process of composition. Czerny would start with one, fill a pair of pages, then progress to the next new work, write a pair of pages of it, and so forth all around the room. By the time he got back around to the first, the ink on its pages would have had time to dry and he could resume work on it.
He is mainly known for his many sets of studies and exercises for piano. These cover virtually every significant issue of technique and interpretation faced by pianists at all levels. Czerny's studies, especially the "School of Velocity, Op. 299," are known (and dreaded) by piano students to this day. It is the endless repetition of them and the fiendish little traps he sets that turns students against Czerny as a composer.
This is unfortunate. Although he was not a particularly original composer, the better of his many essays in creative composition are more than just technically accomplished. They are often witty, imaginative, and charming in ways that surprise.
He never married: He was so driven by the need to compose constantly that he consciously gave up the idea of marriage, or so he said. After his death, writings were found to show that he had an unrequited love for an unknown woman. In the 1840s he health began failing. His unparalleled productivity earned him a respectable estate; he left the bulk of it, on his death, in a series of well-planned bequests to various charities, including the Vienna Gesselschaft der Musikfreunde, the Monks and Nuns of Charity, and (in an apparent tribute to his teacher Beethoven) an institute for the deaf.