Five Americans who had been jailed for years in Iran are flying back home on Monday as a part of a controversial prisoner swap.
The deal - mediated by Qatar - was reached when $6bn (£4.8bn) of Iranian funds held in South Korea reached banks in Doha. The Iranian oil money had been frozen as part of US sanctions.
Five Iranians imprisoned in the US have also been released as part of the swap.
Here is a look at the prisoners from both countries, some of whom are dual-citizens, involved in the exchange.
The American prisoners
Morad Tahbaz (UK-US)
Tahbaz, a 67-year-old business man, was arrested in 2018 along with eight other Iranian conservationists in the midst of the country's crackdown on environmentalists.
The group - members of the Persian Wildlife Heritage Foundation - had been using cameras to track critically-endangered wild Asiatic cheetahs, but were accused of using their environmental projects as a "cover to collect classified information".
Tahbaz and his colleagues have denied the charges against them, and Amnesty International said there was evidence they had been subjected to torture in order to extract forced confessions.
Tahbaz was sentenced to 10 years in prison in 2019.
He was incarcerated in Iran's notorious Evin prison. In March 2022, then-UK Foreign Secretary Liz Truss said Tahbaz had been released from the prison on furlough, but he was returned there just two days later.
United Nations human rights experts said in 2021 that Tahbaz's health had deteriorated during his imprisonment and that he had been denied access to health care.
In August 2023, Tahbaz was taken out of Evin and moved to house arrest.
Siamak Namazi (Iran-US)
The 51-year-old worked as head of strategic planning at the Dubai-based company Crescent Petroleum.
Namazi was arrested by the Revolutionary Guards in October 2015, while his father Baquer, 86, was arrested in February 2016 after Iranian officials granted him permission to visit his son in prison.
They were both eventually sentenced to 10 years in prison by a Revolutionary Court for "co-operating with a foreign enemy state".
Their lawyer has complained that the father and son were denied access to legal representation, held in solitary confinement and suffered health problems. Namazi is also alleged to have been tortured.
In January 2023, Namazi went on a week-long hunger strike to protest against the failure of the US to free him and other dual nationals despite President Joe Biden's promise to make bringing them home a top priority.
He was released to house arrest in August in anticipation of a prisoner exchange agreed to by the US and Iran.
In a statement after his release he thanked Mr Biden for "putting the lives of American citizens above politics" and said he urgently needs to visit an Apple store to replace the devices he lost in Iran.
"I am dying to find out what gadgets now exist - when I was taken hostage, the iPhone 6S had just come out," he said.
Emad Shargi (Iran-US)
Shargi is an Iranian-American businessman who moved to Iran from the US with his wife in 2017.
The 58-year-old was initially detained by the Revolutionary Guards in April 2018 while working for Iranian venture capital fund Sarava. He was released on bail that December, when officials told him that a court had cleared him of spying charges that he had denied.
However, in November 2020, Shargi was summoned by a Revolutionary Court and told that he had been convicted of espionage in absentia and sentenced to 10 years in prison, his family said.
His daughters told the Washington Post in April 2021 that he was "trapped in terrible conditions" in prison and that he had only been allowed a couple of brief, monitored phone calls.
In August 2023, Shargi was also released to house arrest in anticipation of a prisoner exchange between the US and Iran.
Two other Americans who were released as a part of the prisoner swap have not been named.
The Iranian prisoners
Five Iranians imprisoned in US jails, mostly on charges of violating US sanctions, are also being freed as part of the swap, according to Iranian officials. Not all of them are expected to return to Iran.
Mehrdad Moein Ansari (Iran)
Ansari is a 40-year-old resident of the United Arab Emirates and Germany. He was sentenced to 63 months in prison in 2021 for violating sanctions on Iran as a part of a scheme to obtain military-sensitive parts for Iran, according to the US Justice Department.
Prosecutors allege Ansari obtained and tried to obtain parts that could be used in nuclear weapons systems, missile guidance and development.
Justice Department officials said Ansari and co-conspirators "attempted to profit from a far-reaching, extensive scheme to evade U.S. sanctions on Iran. They repeatedly lied to numerous US suppliers and illegally obtained very sensitive dual-use items".
Kambiz Attar Kashani (US-Iran)
In February 2023, 44-year-old Kashani was sentenced to 30 months in prison for conspiring to illegally export US goods and technology to Iran, including to the Central Bank of Iran, which the US government has designated as a supporter of terrorist organisations.
Justice Department officials allege Kashani and his co-conspirators used two front companies in the United Arab Emirates to illegally obtain electronic goods and technology from multiple US companies to send to Iran.
Kashani pleaded guilty to the charges.
Reza Sarhangpour-Kafrani (Canada-Iran)
Kafrani was charged in 2021 with the unlawful export of laboratory equipment from the US to Iran, through Canada and the United Arab Emirates.
Kafrani was living in Montreal and owned a Canada-based company that conducted business in the US and other countries.
US prosecutors allege Kafrani negotiated with a US company to buy mass spectrometry equipment to be shipped to Iran through Canada and the UAE. The US government requires a license to export the equipment to Iran and the UAE.
Amin Hassanzadeh (Iran)
Prosecutors allege Hassanzadeh, a permanent resident of the US, stole sensitive technical data from his employer and then sent it to his brother in Iran, who had connections to the Iranian military.
He was charged in 2019 with interstate transportation of stolen property and fraud.
Prosecutors say the engineer and visiting scholar at the University of Michigan participated in a year-long plan to steal confidential data about an aerospace industry project, allegedly emailing the confidential data to his brother in Iran just days after starting his job.
Kaveh Lotfolah Afrasiabi (US-Iran)
Afrasiabi is an author who was arrested by the FBI at his home in Massachusetts for acting and conspiring to act as an unregistered agent of the Iranian government.
US officials say Iran was paying Afrasiabi to spread propaganda.
"For over a decade, Kaveh Afrasiabi pitched himself to Congress, journalists, and the American public as a neutral and objective expert on Iran," Justice Department officials said in a statement.
"However, all the while, Afrasiabi was actually a secret employee of the Government of Iran and the Permanent Mission of the Islamic Republic of Iran to the United Nations (IMUN) who was being paid to spread their propaganda."
The Justice Department said the author sought to disguise propaganda as objective policy analysis and expertise to influence the public and US policymakers.
They alleged Afrasiabi intentionally "evaded his obligation to disclose who was sponsoring his views".