The Greeks have voted to reject the austerity terms demanded by eurozone creditors - so, what now?
Q: What happens next?
A: Prime Minister Alexis Tsipras has said he will try to negotiate a fresh deal with creditors - the eurozone, the European Central Bank and the International Monetary Fund - within 48 hours.
However, the creditors said that a No vote means the end of negotiations, which could mean the withdrawal of the emergency financial lifeline from the ECB to Greek banks.
Q: What if the creditors refuse to negotiate?
A: There is no legal mechanism for exiting the eurozone.
Some Greek politicians have suggested it could refuse to leave, but the government would be forced to start printing its own currency to keep the country functioning.
One economic analysis suggested that an economy which has already shrunk by 25% since 2008 could contract by another 25%.
Tourism and business could suffer and there are fears of an humanitarian disaster and social unrest as stocks of medicines and fuel run out.
Q: What would a Grexit mean for the rest of the eurozone?
A: There are likely to be huge losses for the European Central Bank, and institutions in eurozone countries that have lent to Greek banks.Doubts about the survival of the currency project could drive down its value and hamper already sluggish economic growth.
Q: Would Britain suffer?
A: The UK is outside the eurozone, and is not liable for any losses by the ECB. British banks, and financial institutions also have very limited direct exposure to Greek debt.
Interest rates on government borrowing could fall and the value of sterling increase as investors seek "safe haven" from the chaos.
But wider "contagion" among financial institutions, falling stock markets and an economic slowdown in the eurozone could be very damaging to the UK's prospects.
Prime Minister David Cameron, Chancellor George Osborne and Bank of England Governor Mark Carney are holding talks on the potential dangers and finalising contingency plans.
Q: Could there still be a deal?
A: Controversial Greek Finance Minister Yannis Varoufakis has resigned in a bid to help Prime Minister Alexis Tsipras secure a deal and the IMF has suggested that it could consider some debt relief.
But banks could start collapsing immediately if they are forced to open again tomorrow without a new line of credit.
The eurozone's two biggest players - German Chancellor Angela Merkel and French President Francois Hollande - are set to meet in Paris today to discuss the way forward.
Merkel has said that new Greek aid talks depend on proposals the country makes.
Q. What about tourists heading for Greece?
A. The official advice is to take euros in cash while banks are closed and to be aware of regular demonstrations and strikes taking place that may disrupt public transport.
The latest advice from the Foreign and Commonwealth Office (FCO) said: "While banks are closed in Greece and some withdrawals are limited, make sure you take sufficient euros in cash to cover the duration of your stay, emergencies, unforeseen circumstances and any unexpected delays.
..."You should take appropriate security precautions against theft."