Steinway & Sons, also known as Steinway (/ˈstaɪnweɪ/ ^ⓘ), is a German-American piano company, founded in 1853 in New York City by German piano builder Heinrich Engelhard Steinweg (later known as Henry E. Steinway). The company's growth led to a move to a larger factory in New York, and later opening an additional factory in Hamburg, Germany. The New York factory, in the borough of Queens, supplies the Americas, and the factory in Hamburg supplies the rest of the world.

Steinway is a prominent piano company, known for its high quality and for inventions within the area of piano development. Steinway has been granted 139 patents in piano making, with the first in 1857. The company's share of the high-end grand piano market consistently exceeds 80 percent. The dominant position has been criticized, with some musicians and writers arguing that it has blocked innovation and led to a homogenization of the sound favored by pianists.

Steinway pianos have received numerous awards. One of the first is a gold medal in 1855 at the American Institute Fair at the New York Crystal Palace. From 1855 to 1862, Steinway pianos received 35 gold medals. More awards and recognitions followed, including three medals at the International Exposition of 1867 in Paris. The European part of the company held a royal warrant of appointment to Queen Elizabeth II. Steinway & Sons was named Company of the Year in 1996 by The Music Trades magazine. The award was given in recognition of Steinway's "overall performance, quality, value-added products, a well-executed promotional program and disciplined distribution which generated the most impressive results in the entire music industry."

In addition to the Steinway piano line, Steinway markets two other, lower-priced brands of piano sold under the brand names Boston and Essex.

Heinrich Engelhard Steinweg first made pianos in the 1820s from his house in Seesen, Germany. He made pianos under the Steinweg brand until he emigrated from Germany to America in 1850 with his wife and seven of his nine children. The eldest son, C. F. Theodor Steinweg, remained in Germany, and continued making the Steinweg brand of pianos, partnering with Friedrich Grotrian, a piano dealer, from 1856 to 1865.

In 1853, Heinrich Engelhard Steinweg founded Steinway & Sons. His first workshop in America was in a small loft at the back of 85 Varick Street in the borough of Manhattan in New York City. The first piano made by Steinway & Sons was given the number 483 because Heinrich Engelhard Steinweg had built 482 pianos in Germany. Number 483 was sold to a New York family for $500, and is now on display at the Städtisches Museum Seesen, the town in which Heinrich Engelhard Steinweg began his career as a piano maker. A year later, demand was such that the company moved to larger premises at 82–88 Walker Street. It was not until 1864 that the family anglicized their name from Steinweg to Steinway.

By the 1860s, Steinway had built and moved into a factory at Park Avenue between 52nd and 53rd Street (the present site of the Seagram Building) where it covered a whole block. With a workforce of 350 men, production increased from 500 to nearly 1,800 pianos per year. The employees were mostly German immigrants and the official language of the company was German. The pianos themselves underwent numerous substantial improvements through innovations made both at the Steinway factory and elsewhere in the industry based on emerging engineering and scientific research, including developments in the understanding of acoustics. Almost half of the company's 139 patented inventions were developed by the first and second generations of the Steinway family. Steinway's pianos won prizes at exhibitions in New York City, London, and Paris. By 1862, Steinway pianos had received more than 35 medals. Part of Steinway's early reputation arose from its successes in trade fairs.

In 1865, the Steinway family sent a letter to C. F. Theodor Steinweg asking that he leave the German Steinweg factory (by then located in Braunschweig (Brunswick)) and travel to New York City to take over the leadership of the family firm due to the deaths of his brothers Henry and Charles from disease. C. F. Theodor Steinweg obeyed, selling his share of the German piano company to his partner Wilhelm Grotrian (son of Friedrich Grotrian) and two other workmen, Adolph Helfferich and H. G. W. Schulz. The German factory changed its name from C. F. Theodor Steinweg to Grotrian, Helfferich, Schulz, Th. Steinweg Nachf. (English: Grotrian, Helfferich, Schulz, successors to Th. Steinweg), later shortened to Grotrian-Steinweg. In New York City, C. F. Theodor Steinweg anglicized his name to C. F. Theodore Steinway. During the next 15 years of his leadership, he kept a home in Braunschweig and traveled often between Germany and the United States.