A fortepiano [ˌfɔrteˈpjaːno] is an early piano. In principle, the word "fortepiano" can designate any piano dating from the invention of the instrument by Bartolomeo Cristofori in 1700 up to the early 19th century. Most typically, however, it is used to refer to the mid-18th to early-19th century instruments, for which composers of the Classical era, such as Haydn, Mozart, and the younger Beethoven and Schubert, wrote their piano music.

Starting in Beethoven's time, the fortepiano began a period of steady evolution, culminating in the late 19th century with the modern grand. The earlier fortepiano became obsolete and was absent from the musical scene for many decades. In the later 20th century, the fortepiano was revived, following the rise of interest in historically informed performance. Fortepianos are built for that purpose, in specialist workshops.

The fortepiano has leather-covered hammers and thin, harpsichord-like strings. It has a much lighter case construction than the modern piano and, except for later examples of the early nineteenth century (already evolving towards the modern piano), it has no metal frame or bracing. The action and hammers are lighter, giving rise to a much lighter touch, which in well-constructed fortepianos is also very expressive.

The range of the fortepiano was about four octaves at the time of its invention and gradually increased. Mozart wrote his piano music for instruments of about five octaves. The piano works of Beethoven reflect a gradually expanding range; his last piano compositions are for an instrument of about six and a half octaves. The range of most modern pianos, attained in the 19th century, is 7⅓ octaves.

Fortepianos from the start often had devices to change the resonance like the pedals of modern pianos, but they were not always pedals: sometimes hand stops or knee levers were used instead.

Like the modern piano, the fortepiano can vary the sound volume of each note, depending on the player's touch. The tone of the fortepiano is quite different from that of the modern piano, however, being softer, with less sustain. Sforzando accents tend to stand out more than on the modern piano, because they differ from softer notes in timbre as well as volume, and decay rapidly.

Fortepianos also tend to have quite different tone quality in their different registers – slightly buzzing in the bass, "tinkling" in the high treble, and more rounded (closest to the modern piano) in the mid range. In comparison, modern pianos are rather more uniform in tone through their range.

The piano was invented by the harpsichord maker Bartolomeo Cristofori in Florence. The first reliable record of his invention appears in the inventory of the Medici family (who were Cristofori's patrons), dated 1700. Cristofori continued to develop the instrument until the 1720s, the time from which the surviving three Cristofori instruments date.