Madeleine was three when she disappeared from her bedroom during a 2007 family holiday in Portugal, while her parents, Kate and Gerry, were eating at a nearby tapas restaurant with friends.
Her disappearance, which has since been declared a murder investigation by German police, has become one of the most high-profile missing person cases in history.
What are the latest developments?
Police are continuing to investigate German national Christian Brueckner - also known an Christian B - as an official suspect in the disappearance of Leicestershire toddler Madeleine McCann.
Portuguese authorities have not formally named him, but are acting on the request of German authorities.
ITV News has received confirmation the formal suspect is Christian Brueckner, the man German police first said they were investigating in 2020.
In May 2023, German authorities were expected to fly to Portugal to conduct fresh searches of a site identified in the search for Madeleine.
The search is due to take place at a dam 50km from Praia Da Luz, where Madeleine went missing and Christian Brueckner spent a number of years living.
Has he been charged?
No, he has not been charged and denies any involvement in Madeleine's disappearance.
What did we know about him before?
German media named Christian Brueckner (whom they only refer to as 'Christian B.' due to the country's strict privacy laws) as a suspect on June 4, 2020.
The convicted German child sex offender is currently in prison in his home country, serving a prison sentence for a sex crime.
'It's not apparently based on any more evidence' - journalist Natasha Donn tells ITV News naming Christian B as an official suspect is a 'stalling move'
He has two previous convictions for "sexual contact with girls".
He lived in the Portuguese coastal village of Praia da Luz on and off between 1995 and 2007.
Where and when did Madeleine McCann go missing?
The three-year-old disappeared from her room in the family's holiday apartment in the Portuguese village of Praia da Luz on May 3, 2007.
When was she discovered to be missing?
On the night of her disappearance, her parents Kate and Gerry McCann left their three children asleep in their holiday apartment while they went to a nearby tapas restaurant with friends.
The parents and their friends were taking turns to check on the children.
When Mrs McCann checked on them at about 10pm, she found Madeleine missing.
What happened next?
Fears quickly grew that Madeleine has been abducted. Sniffer dogs were brought in, the Spanish and border police and airports were notified and volunteers searched the village, beach and resort.
Jane Tanner, one of the friends dining with the McCanns, reported having seen a man carrying a child earlier that night.
Was anyone arrested?
On May 14, 2007, detectives took in property developer Robert Murat for questioning and police searched the home he shared with his mother - just 100 yards from where the three-year-old vanished.
He was made an 'arguido', or formal suspect, although this was later withdrawn.
In September, during questioning of Mr and Mrs McCann, detectives made them both 'arguidos' in their daughter's disappearance, but this was also later withdrawn.
What happened to the original investigation by the Portuguese police?
The Portuguese authorities shelved their investigation in 2008 and lifted the 'arguido' status on the McCanns and Robert Murat.
Then, three years later, Scotland Yard opened a review into the case at the request of then-home secretary, Theresa May.
The following year, detectives said they believed Madeleine could still be alive and released an age-progression picture of how she might look as a nine-year-old.
London called on the Portuguese authorities to reopen the case, but the country's police said they had found no new material.
But, in October 2013, Portuguese police did re-open their case after a review of their original investigation uncovered new lines of inquiry.
What was Scotland Yard's Operation Grange?
Two years into a review of the case, Scotland Yard launched its own investigation into Madeleine's disappearance.
They claimed to have "genuinely new" lines of inquiry and identified 38 people of interest, including 12 Britons.
Operation Grange received £12.3 million in funding up to April 2020, and, despite a more than £10 million investigation, no one was ever charged in connection with Madeleine's disappearance.
Want a quick and expert briefing on the biggest news stories? Listen to our latest podcasts to find out What You Need To Know...