The last independence referendum was only five years ago, but the political and economic has changed across Scotland in a number of areas:
The crash in the North Sea oil and gas industry of recent years dealt a shattering blow to Scotland's economy and undermined one of the key arguments at the heart of the campaign for independence. Tens of thousands of jobs were shed as firms cut back in a radical period of readjustment. The situation has evened out now and the oil and gas related services industry is still a massive and critical part of Scotland's "real" economy. But corporation tax receipts were worth barely £1 billion UK-wide last year - the SNP had been predicting up to £7.9 billion in North Sea taxes for the Scottish Treasury in the first years of independence. And with global prices stuck at about $70 a barrel - down from over $110 at the start of the decade - and new exploration flatlining, revenues are unlikely to reach those previous heights again.
This is the difference between money spend on public services like schools and hospitals and the taxes raised to fund them. In 2014 the Scottish Government had predicted a deficit of up to £5.5 billion, including historic debt payments to the UK. However, the latest official Scottish Government GERS (Government Expenditure and Revenue Scotland) showed that Scotland's deficit is closer to £10.3 billion. This is 6% of GDP and about three times the UK level. The SNP's revised economic case for independence seeks to half this and calls for public spending restraints until this is achieved, but has been branded recipe for enhanced austerity by activists.
One things which has remained relatively stable in recent years has been support for independence at about the 45% level it was in the last vote . Two recent polls even suggested this was closing, with a Panelbase survey for the Sunday Times putting it as high as 49%. This has been behind the growing grassroots pressure on Nicola Sturgeon for a bold approach - that "one last push" could get the Yes campaign over the line. Pro-union supporters, though, say there is less chance of movement in the polls this time, as so many voters made up their minds on the issue last time round.
The EU slammed the door in the face of the Nationalist side in Scotland at the last referendum, making it clear that an independent Scotland would find itself outside the EU and forced to "get in the queue" and rejoin as a new state, a process that can take years. This flatly contradicted the Yes campaign's claim that Scotland's EU membership would be uninterrupted by leaving the UK. However, attitudes have changed in the aftermath of the Brexit vote and EU leaders may be privately content to see the UK break up outside it ranks. A number of leading EU figures, including Belgian MEP Guy Verhofstadt, who was head of the influential liberal group in Brussels have now indicated an independent Scotland would be welcomed in.
Nicola Sturgeon was at the heart of the 2014 referendum campaign, but it was her more combative predecessor Alex Salmond who was the figurehead of the independence push. His garrulous style was doubtless a factor in the often fractious and divisive debate which characterised much of the campaign. Ms Sturgeon herself was involved in may ill-tempered TV debates with political opponents, but has appealed for a more collegiate and measured approach this time to win over wavering No voters who could sway the result.