The path for Greece to leave the euro zone (if that is what eventually happens) is unlikely to be smooth.
In the chart below, we outline some of the different forms a so-called Grexit could take, whether the result of this Sunday's crucial referendum is a "yes" or "no" to the complicated question being asked of the Greek people.
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The vote is, on the surface, on the proposals put forward by Greece's international creditors last Thursday, which are no longer on the table. The referendum is being viewed more widely, however, as a vote on continued membership of the euro zone. Euro zone leaders including European Commission President Jean Claude Juncker have backed up the view that the vote is essentially on euro zone membership and asked Greeks to vote "yes," "whatever the question."
While Greek Prime Minister Alexis Tsipras insists the country could vote "no" and stay within the euro zone, it is difficult to see how other members of the single currency could reconcile a Greece which does not make its debt repayments, but stays in their club.
If there is a "yes" vote, the problem of whether Greece can continue to repay its debts without a major haircut and a plan to stimulate economic growth remains.
Ratings agency Standard & Poor's now believes the probability that Greece will exit the euro zone is around 50 percent.
"A Grexit would be such a unique event that we cannot discount a scenario that could bring severe contagion and long-term damage to political cohesiveness," Standard & Poor's credit analyst Lapo Guadagnuolo warned in a research note.
- By CNBC's Catherine Boyle