What exactly have the two sides admitted to?
The 10 Russian spies have conceded rather less than their American counterparts. In exchange for a pardon from President Dmitry Medvedev, the four men released by Russia have signed statements admitting they were full-blown spies, though apparently at least one of them did so with great reluctance. The 10 caught in the US, on the other hand, pleaded guilty only to conspiracy to act as agents of a foreign country. Much weightier charges were set aside in the interests of making the deal.
What will happen to them now?
One thing is absolutely clear: those released are highly unlikely to be actively involved in espionage in the future. The operatives on both sides have admitted guilt as part of the exchange, and none of the Russians will be allowed back into the United States without the special permission of the Attorney General.
Instead, they will probably seek a quiet life out of the public eye. In Russia, former operatives are often given a lifelong stipend by the state, and at least one of the returning "illegals" has been promised about $2,000 (£1,300) a month; they will also be free to go wherever they choose, as long as it is not the US. Their children were reported to be leaving the US to join them last night.
The men freed in Moscow have varying fates. Whereas Alexander Zaporozhsky's family are already in the US, and Gennady Vasilenko has business contacts in the US, Igor Sutyagin may be much less at home in his adopted nation. Meanwhile, Sergei Skripal, who was jailed for working for MI6, is expected to settle in the UK.
Will we ever hear their stories?
It is highly unlikely: as a condition of their release, the 10 who were held in the US have agreed to forfeit any proceeds from selling their stories to the American government. The four freed by Russia, on the other hand, are perhaps not well known enough to find their lives on the front pages or the silver screen.
How was the deal struck?
With extreme speed. Analysts say that similar deals made during the Cold War era took far longer to iron out. Much of the credit for the rapid closure has gone to the US Under-Secretary of State, William Burns, a former Ambassador to Moscow, and the Russian Ambassador to the US, Sergei Kislyak, who met in Washington on Wednesday. The CIA chief, Leon Panetta, and his SVR counterpart, Mikhail Fradkov, also met for talks. According to US officials, the Russian government initially denied knowledge of the agents, before changing their stance for the sake of a deal. Presidents Obama and Medvedev never spoke about the matter directly, but were briefed on negotiations throughout.
Why was it worth making?
Both sides have come in for criticism for striking a deal that arguably does less than before to deter foreign operatives from working on their soil. But for the US, the limited success of the "illegals" meant that they pose no future national security threat, and the risk of derailing relations with Moscow was simply not worth taking. And in Russia, the chance to turn an embarrassingly public defeat into a score draw at the very least must have seemed worthwhile – even at the cost of four heavyweight operatives in exchange for such apparently minor players.