Bonhams is a privately owned international auction house and one of the world's oldest and largest auctioneers of fine art and antiques. It was formed by the merger in November 2001 of Bonhams & Brooks and Phillips Son & Neale. This brought together two of the four surviving Georgian auction houses in London, Bonhams having been founded in 1793, and Phillips in 1796 by Harry Phillips, formerly a senior clerk to James Christie.

Today, the amalgamated business handles art and antiques auctions. Bonhams operates two salerooms in London—the former Phillips saleroom at 101 New Bond Street, and the old Bonham's saleroom at the Montpelier Galleries in Montpelier Street, Knightsbridge—with a saleroom in Edinburgh. Sales are also held around the world in New York, Hong Kong, Los Angeles, Paris, Boston, San Francisco, and Sydney. Bonhams holds more than 450 sales a year in more than 60 collecting areas, including Asian art, pictures, cars and jewellery. Bonhams has more than 1,000 staff with some of the world's leading specialists in their fields.

Bonhams was set up in 1793 when Thomas Dodd, an antique print dealer, joined with the book specialist Walter Bonham. The company expanded and by the 1850s was handling all categories of antiques including jewellery, porcelain, furniture, arms and armour, and wine. After returning from the war, in the early 1950s, Leonard Bonham purchased some land in Knightsbridge and erected a saleroom on Montpelier Street. The first sale was held in June 1956.

In 2000, Bonhams became Bonhams & Brooks when it was acquired by Brooks auction house. Brooks had been founded in 1989 by the former Head of Cars at Christie's, Robert Brooks who specialized in the sale of classic and vintage motorcars. Brooks continued a major acquisition programme aimed at creating a new international fine art auction house.

In 2001 Bonhams & Brooks merged with Phillips Son & Neale to form a new UK company trading as Bonhams. Phillips Son & Neale had been based in 101 New Bond Street, which subsequently became the new headquarters of Bonhams. The building consisted of seven different freeholds and had been described as "a Dickensian rabbit warren". The first of the sites to be acquired was Blenstock House, an Art Deco building at the junction of Blenheim Street and Woodstock Street, eventually acquiring the complete building in 1974.

Acquisition activity continued, and in 2002 Bonhams purchased Butterfields, a leading auction house on the West Coast founded in 1865. Bonhams changed Butterfields' name to Bonhams & Butterfields, and Malcolm Barber, formerly of Brooks, became the chief executive officer of the American subsidiary. Bonhams remained the company's brand name outside of the United States.

By the end of 2003 Bonhams was conducting more than 700 annual sales with revenues of $304 million. The company's worldwide network of sales included two major London venues, nine additional UK locations, and salerooms in Australia, Switzerland, Monaco, Germany and the US. Bonhams & Butterfields conducted its first East Coast sale in 2003 with an auction of Edwin C. Jameson's collection of classic cars and antiques in Massachusetts, US.

During 2005, Bonhams expanded further with the opening of the Paris office and a new saleroom in New York.