D-274 (or D) is the model name of a concert grand piano, the flagship of the Steinway & Sons piano company, first built in 1884. It is generally described as the first choice of most concert pianists. As of 2017 a D-274 finished in Polished Ebony has a MSRP of US$175,700.

At 274 centimetres (9 ft 0 in) long, 156 centimetres (5 ft 1 in) wide and 480 kilograms (1,060 lb), the D-274 is too large for most homes. In concert hall settings, on the other hand, the D-274 is a major presence. An example would be the famous Van Cliburn International Piano Competition, which offers contestants a choice of two D-274s owned by the Van Cliburn Foundation, one a mellow-toned instrument made in New York, the other a bright-toned instrument made in Hamburg. These are supplemented with a third Steinway piano brought in for the event.

An estimate from 2003 suggested that more than 90 percent of concert grand pianos worldwide are D-274s.

Virtually all critical design elements of the Steinway 'D' were developed during the 19th century. Among them are the action and string scale designs perfected by Henry Steinway Jr., the company founder's son; the hammers, cast iron frame and laminated wooden rim, all originating in designs patented by C. F. Theodore Steinway, another of the founder's sons; the trapwork (pedals), first devised by Albert Steinway, a third son; and most aspects of the soundboard. Since those early years, only two notable improvements to the model have been made: a concentric shaping of the soundboard, a design patented by younger family member Paul Bilhuber, was introduced in 1936; more recently the action was changed to provide a greater mechanical advantage to the player, resulting in less touch resistance with no loss of power.

Even before the German-born family emigrated to the United States, the founder, Henry E. Steinway, had built a grand piano in 1836 (the so-called "kitchen grand"), which today is preserved at the Steinway Hall in New York City. Such grand pianos with a limited keyset of 6 or 6.5 octaves and double strings produce less volume of sound than a D-type concert grand piano.

Concert grand pianos of full size are able to fill a concert hall with sound for 2,000 to 3,000 spectators. This was foreshadowed in the 1860s when grand pianos were given harps or frames of cast iron. Initially employed to accommodate the cumulative and extraordinary tension of the strings, thereby protecting the wooden structure from destruction, iron frames quickly facilitated a dramatic increase in string tension. With increased string tension came increased power and projection.

At the 1876 Centennial Exposition in Philadelphia, Pennsylvania, there were several manufacturer's competitions, including a piano competition. The Steinway company sent two grand pianos displaying their latest developments, demonstrating the firm's innovative and markedly improved piano quality. Their determined pursuit of quality was rewarded at the world exhibition with a gold medal. Steinway won the competition against several established, well-known American piano makers, including Chickering & Sons and Weber Piano Company.

This Steinway concert grand piano, the direct predecessor of today's Model 'D', has become known as the "Centennial grand". It remained in production until 1878, when improvements prompted the Steinways to re-designate their models, replacing numeric designations (Types 1 through 4) with Model letters, i.e., A, B, C and D. These letters still mark the types of Steinway's four largest instruments.