British girl Madeleine McCann vanished, when aged three, from a Portuguese holiday apartment in May 2007.
A Portuguese police investigation which ran until July 2008, and a continuing high-profile international campaign run by her parents Kate and Gerry, have failed to locate her.
Scotland Yard announced it was launching an investigation into Madeleine's disappearance in July 2013 - after spending two years reviewing the case.
On 24 October 2013 it was announced that the Portuguese police had reopened their inquiry into the disappearance, citing "new lines of inquiry". The Scotland Yard inquiry will run alongside the Portuguese investigation.
Madeleine McCann, from Rothley, Leicestershire, went missing from her family's holiday apartment at the Ocean Club, in Praia da Luz, on 3 May, 2007.
Her parents had gone for dinner with a group of seven friends at a tapas restaurant 100 yards from the apartment, but when her mother, Kate, went to check on Madeleine and her younger brother and sister later in the evening, Madeleine was gone.
Police were called and about 60 staff and guests at the complex searched until daybreak for the little girl, while police notified border police, Spanish police and airports.
Hundreds of volunteers joined in the search for Madeleine in the days after.
Timeline of events
5 May: The McCanns issue a statement saying they "cannot describe the anguish and despair" they are feeling. Portuguese police say they have a suspect in mind. They believe Madeleine was abducted but is still alive and in Portugal.
12 May: The couple make a fresh appeal for help on their daughter's fourth birthday.
15 May: British-born Robert Murat is made an official suspect - or "arguido" - following a search of his mother's villa. Casa Liliana is 150 yards from the McCanns' holiday apartment.
26 May: Police issue a description of a man seen on the night Madeleine went missing "carrying a child or an object that could have been taken as a child".
17 June: Chief Inspector Olegario Sousa admits vital forensic clues may have been destroyed in the hours after Madeleine's disappearance as the scene was not protected properly.
Late July: British sniffer dogs flown out to Portugal. Keela, who can detect minute quantities of blood, and Eddie, who is trained to detect bodies, work in the apartment and several cars, including the hire car the McCanns had rented 25 days after Madeleine disappeared.
11 August: One hundred days after Madeleine disappeared, investigating officers publicly acknowledge she could be dead. Police say Mr and Mrs McCann are not being considered as suspects following newspaper speculation that they are under suspicion.
31 August: The McCanns launch a libel action against Portuguese newspaper Tal & Qual which claimed "police believe" they killed their daughter. The McCanns say they are "deeply hurt" by the allegations.
6 September: Portuguese police interview Kate McCann for 11 hours as a witness in the presence of her lawyer.
7 September: During further questioning of Mr and Mrs McCann, detectives make them both "arguidos". Later, a family representative says officers believe they have found traces of Madeleine's blood in the McCanns' hire car.
9 September: Kate and Gerry McCann return home to Rothley, Leicestershire.
11 September: Portuguese police play down reports that DNA evidence with a 100% match to Madeleine was found in her parents' hire car.
19 September: Portuguese prosecutors rule there is "no new evidence" in police files to justify re-questioning Gerry and Kate McCann.
3 October: Goncalo Amaral, the detective in charge of the inquiry, is removed from the case after criticising the British police in a Portuguese newspaper interview.
9 October: Paulo Rebelo, deputy national director of the Portuguese police, is appointed to take over the Portuguese inquiry.
18 November: Gerry McCann, in a personal video, speaks of his belief that his family was watched by "a predator" in the days before his daughter's disappearance.
20 January: The McCanns release sketches of a man they believe may have abducted their daughter. The drawings are based on a description by a British holidaymaker of a "creepy man" seen at the resort.
19 March: Mr and Mrs McCann accept £550,000 libel damages and front-page apologies from Express Newspapers over allegations they were responsible for Madeleine's death.
7 April: Portuguese police fly to the UK to sit in on interviews conducted by Leicestershire Police of the so-called "tapas seven".
14 April: Portuguese police deny leaking details of statements given by the McCanns early in the investigation. Spanish television broadcasts quotes, including some made by Mrs McCann, supposedly telling officers that Madeleine had been upset the night before she disappeared that her mother had not come to her when she cried.
3 May: A tearful Mrs McCann urges people to "pray like mad" for Madeleine as the family mark the first anniversary of the little girl's disappearance.
7 May: Alipio Ribeiro, the Portuguese police chief criticised for his handling of the case, resigns.
1 July: Portuguese police say they have submitted their final report on the case, which the attorney general says "will be the object of careful analysis and consideration".
15 July: British expat Robert Murat accepts a £600,000 damages settlement over allegations in 11 UK newspapers that he was involved in Madeleine's disappearance.
21 July: The Portuguese authorities shelve their investigation and lift the "arguido" status of the McCanns and Mr Murat.
24 July: Mr Amaral publishes a book about the case, entitled The Truth of the Lie, in which he alleges that Madeleine died in her family's holiday flat.
16 May: The McCanns say they will sue Mr Amaral over comments he made in the media.
3 November: A one-minute video message - produced in seven languages - is launched by Britain's Child Exploitation and Online Protection Centre, showing new images of how Madeleine might look more than two years older.
6 March: The McCanns criticise the release of previously unseen Portuguese police files on their daughter's case to British newspapers. The 2,000-page dossier details dozens of possible sightings of Madeleine since her disappearance.
28 April: Near the third anniversary of Madeleine's disappearance, Gerry McCann says it is "incredibly frustrating" that police in Portugal and the UK had not been actively looking for Madeleine "for a very long time".
August: Kate and Gerry McCann hold private talks with Home Secretary Theresa May.
November: The McCanns sign a publishing deal to write a book about their daughter's disappearance. They also launch a petition calling for a full review of the case by the UK and Portugal.
12 May: In an open letter in the Sun newspaper, the McCanns ask the prime minister to launch an "independent, transparent and comprehensive" review of all information relating to Madeleine's disappearance.
They publish a book, entitled Madeleine, which they hope will prompt people holding vital information about what happened to Madeleine to come forward. Sale proceeds will go towards the Find Madeleine fund.
13 May: Prime Minister David Cameron writes to the McCanns telling them the home secretary will be in touch to set out "new action" involving the Metropolitan Police.
6 September: The McCanns are among alleged victims who request to be "core participants" in the first part of the Leveson Inquiry into the phone-hacking scandal.
9 September: British detectives reviewing the search for Madeleine hold their first face-to-face meetings with Portuguese police chiefs.
16 November: Lawyer David Sherborne tells the Leveson Inquiry the treatment of the McCanns by the press was a "national scandal".
23 November: The McCanns tell the Leveson Inquiry they were left distraught by press suggestions they were responsible for Madeleine's death.
12 January : Daily Star editor Dawn Neesom tells the Leveson Inquiry that she regrets the paper's coverage of Madeleine's disappearance.
24 April: The detective leading the UK review of Madeleine's disappearance says they have the "best opportunity" yet to find her. Det Ch Insp Andy Redwood tells BBC's Panorama his team are "seeking to bring closure to the case".
25 April: Detectives reviewing evidence issue a computer-generated image of what she might look like aged nine.
26 April: Portuguese authorities say they are not reopening their investigation.
17 May: UK detectives reviewing the case say they have identified "a number of persons of interest".
4 July: The Metropolitan Police says it has new evidence and has opened a formal investigation. It says it is investigating 38 "persons of interest".
12 September: A £1m libel case against former Portuguese police chief Goncalo Amaral begins in Lisbon.
4 October: Scotland Yard detectives say mobile phone records may hold the key to solving the case. There are 41 potential suspects, they say.
14 October: A BBC Crimewatch appeal features e-fit images of a man seen carrying a blond-haired child of three or four, possibly wearing pyjamas, in Praia da Luz at about the time Madeleine went missing. It also shows a detailed reconstruction of events on the night she disappeared.
24 October: Portuguese police reopen their inquiry into Madeleine's disappearance, citing "new lines of inquiry". The Scotland Yard inquiry will run alongside the Portuguese investigation.