In a startling intervention the former US president has called on the Scots to reject independence and stay with Britain.
His call was released by the ”Better Together”organization and was portrayed as a last minute surprise to lure undecided voters.
Observers believe his close links with former Prime Minister Gordon Brown, who is de facto leading the "no" vote effort, may have influenced the move.
The final opinion polls show an incredibly close race with the "no" side leading by about two points.
Women are far more likely to vote against independence than men, say pollsters, but there are still an extraordinary number who are undecided – about ten percent on the eve of polling.
Clinton said: "With so much turmoil and division across the globe, I hope the Scots will inspire the world with a high turnout and a powerful message of both identity and inclusion.
"I understand and sympathise with those who want independence. Scotland is blessed with impressive human and natural resources and a strong desire for more widely shared prosperity and social solidarity.
"However, I hope the Scots people will vote to remain in the UK for several reasons:
"1. The proposal to keep the pound as its currency without the support that UK membership provides carries substantial risks, as we saw in the EU after the financial crisis.
"2. Separation will require a long, complex negotiating process with considerable uncertainty and potential to weaken the Scottish economy.
"3. The increased autonomy promised Scotland by the UK provides most of the benefits of independence and avoids the downside risks.
"4. Unity with maximum self-determination sends a powerful message to a world torn by identity conflicts that it is possible to respect our differences while living and working together. This is the great challenge of our time. The Scots can show us how to meet it."