The controversial whistle-blowing site Wikileaks is releasing a cache of 251,287 secret messages sent by US diplomatic staff.
Wikileaks is working its way through publication of the files, which have been given in full to five media groups, including the New York Times and Guardian newspapers.
Below are some of the key issues the documents have revealed so far, in alphabetical order.
Afghanistan: Karzai and corruption
Cables from Karl Eikenberry, the US ambassador to Afghanistan, reveal concern among both US and other foreign dignitaries about the fitness of President Hamid Karzai to govern.
In a July 2009 cable released by the Guardian, Mr Eikenberry describes Mr Karzai as "a paranoid and weak individual unfamiliar with the basics of nation-building", and who is "overly self-conscious" that he might be losing favour among the international community.
But he is also considered an "ever-shrewd politician who sees himself as a nationalist hero".
Several Afghan and foreign officials also refer to Mr Karzai as "weak" or losing his influence.
Mr Eikenberry also writes of widespread corruption among Afghan officials, citing examples of large amounts of cash being taken out of the country.
In an October 2009 report, he says Mr Karzai's brother, Ahmad Wali Karzai, is "widely understood to be corrupt and a narcotics trafficker" and advises that his requests for funding for large-scale projects "should be viewed with a healthy dose of scepticism".
Baltic defence plan
In January, US Adm James Stavridis, Nato's top commander in Europe, proposed drawing up defence plans for the three ex-Soviet Baltic states - Estonia, Latvia and Lithuania - against Russian threats, according to a cable signed by US Secretary of State Hillary Clinton and now published by the Guardian.
The policy was put to top military officials from the alliance's 28 members at a meeting in Brussels.
"On January 22 Nato's military committee agreed… under a silence procedure," the cable notes, referring to a decision carried by consensus unless someone speaks up to object.
The state department ordered an information blackout when the decision was taken. Since January the plan has been refined.
Nine Nato divisions - British, German, Polish and US - were identified for combat operations, according to a leak to Poland's Gazeta Wyborcza, the Guardian says.
Another state departement cable sent on 26 January states that "a public discussion of contingency planning would also likely lead to an unnecessary increase in Nato-Russia tensions, something we should try to avoid".
China: Missiles and hacking
In November 2007, the US urged Beijing to stop the shipment of ballistic missile components from North Korea to Iran, according to a cable released by the Guardian.
The goods were being moved through Beijing, and Washington demanded a "substantive response" to their request.
"We assess that the best way to prevent these shipments in the future is for Chinese authorities to take action... that will make the Beijing airport a less hospitable transfer point," the cable states.
China was also cited in another cable, reported in the New York Times, over concern at its alleged growing use of large-scale computer hacking.
The cable claims that a network of hackers and private security experts has been employed by China since 2002 and that it has hacked into US government and business computers, those of Western allies and the Dalai Lama.
The cable quotes a "Chinese contact" telling the US embassy in Beijing that the Chinese government had been behind the hacking of Google's computer systems in the country in January.
Germany: Rendition row
In 2004, a German citizen was snatched in Macedonia and allegedly taken to a secret prison by the CIA. Agents had apparently mistaken him for an al-Qaeda suspect.
A 2007 cable from the US embassy in Berlin details the efforts the US made to persuade Germany not to issue international arrest warrants for the CIA agents accused of involvement.
In an account of a high-level meeting between US and German officials, the cables states that US diplomats "pointed out that our intention was not to threaten Germany, but rather to urge that the German government weigh carefully at every step of the way the implications for relations with the US".
The cables appear to reveal discussions between various countries on whether they would take prisoners released from the Guantanamo Bay detention facility.
Slovenia is offered the chance to meet President Barack Obama if it takes a prisoner, while Kiribati, in the South Pacific, is offered millions of dollars of incentives. Brussels is told taking prisoners could be "a low-cost way for Belgium to attain prominence in Europe".
Other dispatches suggest Beijing was angered by the refusal by the US to send Uighur prisoners from Guantanamo back to China, with their ambassador to Kyrgyzstan calling the move "a slap in the face". Germany and Finland were allegedly warned by China of damage to bilateral relations if they agreed to take in any of the prisoners.
Iran: Nuclear attack calls
Several Arab leaders and their representatives are quoted as urging the US to carry out an attack on Iran to bring an end to its suspected nuclear weapons programme.
In a cable from April 2008, the Saudi ambassador in Washington, Adel al-Jubeir, recalled King Abdullah's "frequent exhortations" to the US to attack Iran.
Mr al-Jubeir said the king wanted the US "to cut the head off the snake"; the cable also reported that the Saudi foreign minister was less extreme, calling for more severe sanctions on Tehran.
During a meeting between King Hamad bin Isa al-Khalifa of Bahrain and US General David Petraeus, the king told the US to stop Iran's nuclear programme "by whatever means necessary".
"The danger of letting it go on is greater than the danger of stopping it," he is quoted as saying in the cable from ambassador Adam Ereli, dated November 2009.
In a 2006 cable, the crown prince of Abu Dhabi, Sheikh Mohammad bin Zayed, told the US he believed Iranian President Mahmoud Ahmadinejad was "going to take us to war".
Meanwhile, Israel's Defence Minister Ehud Barak used a May 2009 visit by a Congressional delegation to Tel Aviv to warn that time was running out to stop Iran's nuclear programme.
"Barak estimated a window between six and 18 months from now in which stopping Iran from acquiring nuclear weapons might still be viable," says a cable sent back to Washington by the US ambassador the following month.
"After that, he said any military solution would result in unacceptable collateral damage."
Koreas: China's relations
Beijing was growing frustrated with North Korea's behaviour, with a Chinese ambassador warning that Pyongyang's nuclear programme was "a threat to the whole world's security".
Many Chinese officials were starting to think that the Korean peninsula should be reunified under Seoul's control, according to South Korean officials.
They added that China was ready to "face the new reality" that North Korea had little value to Beijing as a buffer state.
Chinese Vice Foreign Minister He Yafei allegedly said Pyongyang was behaving like a "spoiled child".
US and South Korean officials have discussed plans for a united Korea, should North Korea collapse.
The US ambassador in Seoul said South Korea would consider offering commercial incentives to China to "help salve" Beijing's "concerns about living with a reunified Korea".
Mexico: Drug war
One cable expresses concern that the Mexican army was failing in its fight against drug cartels, describing the army as "slow and risk averse."
It said troops were not trained to patrol the streets or gather evidence to convict those detained.
However, the Mexican government was praised for its "unprecedented commitment" to take on the drugs gangs.
But the fight is being hampered by widespread "official corruption" and a lack of co-ordination.
According to the cable dated 29 January 2010, the deployment of troops in Ciudad Juarez - a border city at the heart of the drugs war - had failed to reduce violence.
Pakistan: Nuclear fears
US and UK diplomats feared Pakistan's nuclear material could fall into the hands of terrorists, the Guardian reports some of the leaked cables as revealing.
Cables reported in the New York Times reveal the US has been attempting to remove highly enriched uranium from a research reactor in Pakistan since 2007.
In a May 2009 cable, US ambassador Anne W Patterson says Pakistan had refused a visit from US experts. She quotes Pakistan officials as saying removing the fuel would be seen in Pakistan "as the United States taking Pakistan's nuclear weapons".
Another cable concerning a US intelligence briefing in 2008, reported in the Guardian, said Pakistan was "producing nuclear weapons at a faster rate than any other country in the world".
Russian foreign ministry official Yuri Korolev feared that Islamists might infiltrate the ranks of the 120,000-130,000 people directly involved in Pakistan's nuclear and missile programmes.
"There is no way to guarantee that all are 100% loyal and reliable," he told US officials in February, according to the Guardian.
The Gulf state of Qatar, which has hosted the American military for years, is described as the "worst in the region" for anti-terrorism, according to a state department cable from last December.
The cable, reported in the New York Times, said Qatar's security service was "hesitant to act against known terrorists out of concern for appearing to be aligned with the US and provoking reprisals".
Russia: 'Virtual mafia state'
Russia is accused of being a corrupt, autocratic kleptocracy centred on the leadership of Prime Minister Vladimir Putin.
One cable details a briefing for US officials on 13 January 2010, in which a Spanish prosecutor who has specialised on the activities of the Russian mafia in Spain, Jose "Pepe" Grinda Gonzalez, says he considers Belarus, Chechnya and Russia to be virtual "mafia states" and said that Ukraine is going to be one.
In another cable from February 2010, the US ambassador in Moscow John Beyrle details the "shadowy world of corrupt business practices" under former Moscow mayor Yuri Luzhkov, "with corrupt officials requiring bribes from businesses attempting to operate in the city".
"The Moscow city government's direct links to criminality have led some to call it 'dysfunctional', and to assert that the government operates more as a kleptocracy than a government," Mr Beyrle writes.
In another message, the UK Foreign Office's Russia director, Michael Davenport, is quoted as calling Russia a "corrupt autocracy".
Mr Putin has denied links to organised crime.
Sri Lanka: 'War crimes'
A cable sent in January 2010 by the US ambassador in Colombo, Patricia Butenis, reveals she believed Sri Lanka's President Mahinda Rajapaksa was responsible for alleged war crimes during the final states of the country's civil war.
As the Tamil Tigers rebel movement was defeated, thousands of Tamil civilians are believed to have been killed in the Jaffna peninsula by government forces.
Ms Butenis said one of the reasons why there was so little momentum towards the formation of a Sri Lankan inquiry into the deaths was that the president and the former army commander, Sarath Fonseka, were behind them.
"There are no examples we know of a regime undertaking wholesale investigations of its own troops or senior officials for war crimes while that regime or government remained in power," she wrote.
"In Sri Lanka this is further complicated by the fact that responsibility for many alleged crimes rests with the country's senior civilian and military leadership, including President Rajapaksa and his brothers and opposition candidate General Fonseka," she added.
Gen Fonseka lost to Mr Rajapaksa in January's presidential election, and was subsequently convicted of corruption by a court martial.
Both men have denied that government troops committed war crimes.
UK: Afghan war
US and Afghan officials believed UK forces were "not up to the task of securing Helmand" without US military support, according to a cable published in the Guardian newspaper.
Other cables relayed Afghan dissatisfaction with how the British troops were conducting operations in the province. President Karzai reportedly said in 2009 that eight years earlier "even Helmand was safe for girls to go school. Now, 4,000 [sic] British soldiers are in Helmand and the people are not safe".
And the governor of Helmand, Gulab Mangal, told a visiting group of Americans, including Vice-President-elect Joseph Biden, that US troops were urgently needed in Sangin as UK troops were seldom leaving their base in the city.
In another cable, US General Dan McNeill, was said to be "particularly dismayed by the British effort" in fighting the drugs trade in Afghanistan.
He is quoted as saying that British forces had "made a mess" of counter-narcotics operations in Helmand by employing the "wrong" tactics.
A deal with the Taliban which allowed British troops to be withdrawn from Musa Qala in 2006, "opened the door to narco-traffickers in that area, and now it was impossible to tell the difference between the traffickers and the insurgents", he added.
UK: Cluster bombs
The UK kept quiet about a loophole allowing the US to continue storing cluster bombs on its territory despite an international ban on the weapons.
A senior Foreign Office official is quoted in a message sent in May 2009.
Britain was among more than 90 countries which signed the Convention on Cluster Munitions (CCM) in December 2008. The treaty bans the use of cluster bombs and prohibits signatories from assisting other countries to use, stockpile or transfer them.
UK: Royal Family
Prince Andrew, the Duke of York, "spoke cockily", allegedly criticising Britain's Serious Fraud Office probe of an arms deal between BAE and Saudi Arabia at a brunch in the Kyrgyz capital Bishkek, in a 2008 cable from the embassy in Bishkek..
He also criticised journalists, "who poke their noses everywhere", for investigating the deal.
The prince said the UK, along with Western Europe and the US were "back in the thick of playing the Great Game" - a reference to the 19th Century struggle between the British and Russian Empires for control of Central Asia.
"And this time we aim to win," he was quoted as saying.
Another cable quoted a senior Commonwealth official as saying Prince Charles, the heir to the throne, "does not command the same respect as the Queen".
UN: US spying
A cable to US diplomats issued under US Secretary of State Hillary Clinton's name tells them to collect "biographic and biometric" information - including iris scans, DNA samples and fingerprints - of key officials at the UN.
The diplomats are also ordered to find credit card details, e-mail addresses and passwords and encryption keys used for computer networks and in official communications.
The officials covered include "undersecretaries, heads of specialised agencies and their chief advisers, top SYG [secretary general] aides, heads of peace operations and political field missions, including force commanders".
At least nine similar directives covering various countries are included in the Wikileaks release, both under the name of Mrs Clinton and her predecessor, Condoleezza Rice.
Various world leaders are covered by the documents - showing the diplomats' less than flattering views of them.
Italian Prime Minister Silvio Berlusconi is referred to as "feckless, vain, and ineffective as a modern European leader" by a US diplomat in Rome.
US diplomats were similarly unimpressed with German Chancellor Angela Merkel, describing her as "risk averse and rarely creative".
Former UK Prime Minister Gordon Brown tried to strike a deal over Gary McKinnon, who is wanted by Washington for hacking into US computer systems, the Guardian newspaper reports. The newspaper goes on to describe the subsequent US rejection of the deal as a "humiliating rebuff".
The head of the Bank of England, Mervyn King, described the current UK Prime Minister David Cameron and Chancellor George Osborne as lacking in experience and criticised their "tendency to think about issues only in terms of politics and how they might affect Tory electorability", the Guardian newspaper reports.
A 2009 cable from the US embassy in Tripoli claims that Libyan leader Muammar Gaddafi "appears to have an intense dislike or fear of staying on upper floors".
The cable also says Col Gaddafi "relies heavily" on his Ukrainian nurse, described as a "voluptuous blonde", and speculates that the two are involved in a romantic relationship.
Zimbabwe Prime Minister Morgan Tsvangirai is praised as a "brave, committed man" in a 2007 cable written by then ambassador in Harare, Christopher Dell.
But the flattery does not last, and Mr Dell goes on to say: "Tsvangirai is also a flawed figure, not readily open to advice, indecisive and with questionable judgement in selecting those around him."
In another cable, a South African minister takes a pot-shot at Zimbabwean President Robert Mugabe, describing him as "the crazy old man".
In 2008, the Moscow embassy described Russian President Dmitry Medvedev as playing Robin to Prime Minister Vladimir Putin's Batman.
The cables also comment on the extremely close relationship between Mr Berlusconi and Mr Putin.
North Korea's Kim Jong-il is a "flabby old chap" suffering from trauma from a stroke, while Iranian President Mahmoud Ahmadinejad is referred to as "Hitler".
Afghan President Hamid Karzai freed dangerous detainees and pardoned suspected drug dealers because they were linked to powerful or historically significant figures, a 2009 dispatch says.
Yemen: Drone attacks
A January 2010 cable records a meeting between Yemeni President Abdullah Saleh and Gen Petraeus, then US commander in the Middle East. The cable shows that the US has been operating clandestine bombing raids on suspected al-Qaeda targets in Yemen, with the approval of the Yemeni government in Sanaa.
Mr Saleh criticises the US use of cruise missiles against targets and says US troops cannot operate on the ground, but gives Gen Petraeus permission for fixed-wing bombers to circle outside Yemeni territory and "out of sight", waiting for target information.
The president is quoted as saying: "We'll continue saying the bombs are ours, not yours," while Deputy Prime Minister Rashad Alimi jokes that he had just "lied" to parliament, by telling them recent air raids in Arhab, Abyan, Shebwa had only been US-made but fired by Yemeni forces.