Basildon Park is a country house situated 2 miles (3 kilometres) south of Goring-on-Thames and Streatley in Berkshire, between the villages of Upper Basildon and Lower Basildon. It is owned by the National Trust and is a Grade I listed building. The house was built between 1776 and 1783 for Sir Francis Sykes and designed by John Carr in the Palladian style at a time when Palladianism was giving way to the newly fashionable neoclassicism. Thus, the interiors are in a neoclassical "Adamesque" style.

Never fully completed, the house passed through a succession of owners. In 1910 it was standing empty and in 1914, it was requisitioned by the British Government as an army convalescent hospital. It was again sold in 1928 and quickly sold again. In 1929, following a failed attempt to dismantle and rebuild the house in the USA, it was stripped of many of its fixtures and fittings and all but abandoned.

During World War II, the house was again requisitioned and served as a barracks, a training ground for tanks, and finally a prisoner of war camp—all activities unsuited to the preservation of an already semi-derelict building. In 1952, a time when hundreds of British country houses were being demolished, it was said of Basildon Park "to say it was derelict, is hardly good enough, no window was left intact and most were repaired with cardboard or plywood."

Today, Basildon Park is as notable for its mid-twentieth-century renaissance and restoration, by Lord and Lady Iliffe, as it is for its architecture. In 1978, the Iliffes gave the house, together with its park and a large endowment for its upkeep, to the National Trust in the hope that "The National Trust will protect it and its park for future generations to enjoy."

In addition to being open to the public, the house has also served as a filming set. It was used as the location for Netherfield Park in the 2005 film Pride & Prejudice, and more recently the 2016 film "Pride and Prejudice and Zombies," as a location for the 2006 movie Marie-Antoinette, and as Lord and Lady Radley's house in the 2009 film Dorian Gray. The interiors of Basildon stood in for the Crawley family's London mansion, Grantham House, on the series Downton Abbey.