Downton Abbey is a British historical drama television series set in the early 20th century, created and co-written by Julian Fellowes. It first aired in the United Kingdom on ITV on 26 September 2010 and in the United States on PBS, which supported its production as part of its Masterpiece Classic anthology, on 9 January 2011. The show ran for fifty-two episodes across six series, including five Christmas specials.

The series, set on the fictional Yorkshire country estate of Downton Abbey between 1912 and 1926, depicts the lives of the aristocratic Crawley family and their domestic servants in the post-Edwardian era, and the effects the great events of the time have on their lives and on the British social hierarchy. These events include news of the sinking of the Titanic (first series); the outbreak of the First World War, the Spanish influenza pandemic and the Marconi scandal (second series); the Irish War of Independence leading to the formation of the Irish Free State (third series); the Teapot Dome scandal (fourth series); and the British general election of 1923 and the Beer Hall Putsch (fifth series). The sixth and final series introduces the rise of the working class during the interwar period and hints at the eventual decline of the British aristocracy.

Downton Abbey has been praised by television critics and received numerous accolades, including a Golden Globe Award for Best Miniseries or Television Film and a Primetime Emmy Award for Outstanding Miniseries or Movie. It was recognised by Guinness World Records as the most critically acclaimed English-language television series of 2011. It earned 27 Primetime Emmy Award nominations after its first two series, the most for any international television series in the awards' history. It was the most watched television series on both ITV and PBS, and became the most successful British costume drama since the 1981 television serial of Brideshead Revisited.

On 26 March 2015, Carnival Films and ITV announced that the sixth series would be the last; it aired on ITV between 20 September 2015 and 8 November 2015. The final episode, the annual Christmas special, was broadcast on 25 December 2015. A film adaptation, a continuation of the series, was confirmed on 13 July 2018 and released in the United Kingdom on 13 September 2019, and in the United States on 20 September 2019. A second feature film, Downton Abbey: A New Era, was released in the United Kingdom on 29 April 2022 by Universal Pictures, and in the United States and Canada on 20 May 2022 by Focus Features. A third and final film set to conclude the series, Downton Abbey: The Grand Finale, was released in the UK on 12 September 2025.

The first series, comprising seven episodes, explores the lives of the fictional Crawley family, the hereditary Earl of Grantham, and their domestic servants at the family estate in Yorkshire region. The storyline centres on the fee tail, or "entail", governing the titled elite, which endows title and estate exclusively to male heirs. Common recovery had been developed in the fifteenth century as a means of ending an entail. This did not stop the practice and in the seventeenth century lawyers developed strict settlement as a means of enforcing entail. The Settled Land Acts 1882 to 1890 finally allowed strict settlements to be broken by agreement with the next heir, except where he was a minor.

As part of the backstory, the main character, Robert Crawley, Earl of Grantham, had resolved his father's past financial difficulties by marrying Cora Levinson, an American heiress. Her considerable dowry is now contractually incorporated into the committal entail in perpetuity; however, Robert and Cora have three daughters and no son.

As the eldest daughter, Lady Mary Crawley had agreed to marry her second cousin Patrick, the son of the then-heir presumptive James Crawley. The series begins the day after the sinking of RMS Titanic on 15 April 1912. The first episode starts as news reaches Downton Abbey that both James and Patrick have perished in the sinking of the ocean liner. The family then learns that a more distant and unknown male cousin, solicitor Matthew Crawley, the son of an upper-middle-class doctor, has become the next heir presumptive. The story initially centres on the relationship between Lady Mary and Matthew, who resists embracing an aristocratic lifestyle, while Lady Mary resists her own attraction to the new heir presumptive.

Of several subplots, one involves John Bates, Lord Grantham's new valet and former Boer War batman, and Thomas Barrow, an ambitious young footman, who resents the former for taking a position he had desired for himself. Bates and Thomas remain at odds as Barrow works to sabotage Bates's every move. After learning Bates had recently been released from prison, Thomas and Miss O'Brien (Lady Grantham's lady's maid) begin a relentless pursuit that nearly ruins the Crawley family in scandal. Barrow – a closeted homosexual man – and O'Brien create havoc for most of the staff and family. When Barrow is caught stealing, he hands in his notice to join the Royal Army Medical Corps. Matthew eventually does propose to Lady Mary, but she puts him off when Lady Grantham becomes pregnant, understanding that Matthew would no longer be heir if the baby is a boy. Cora loses the baby after O'Brien, believing she is soon to be fired, retaliates by leaving a bar of soap on the floor next to the bathtub, causing Cora to slip while getting out of the tub, and the fall resulting in a miscarriage. It is later revealed that the miscarried foetus was a male. Although Lady Mary intends to accept Matthew, Matthew believes her reluctance is due to the earlier uncertainty of his heirship and emotionally rescinds his proposal, leaving Lady Mary devastated. The series ends just after the assassination of Archduke Franz Ferdinand and the outbreak of the First World War in August 1914.