The debate has already begun in Westminster on a timetable for change in Scotland and the rest of the UK.
Prime Minister David Cameron has said English MPs should be the only ones to vote on English matters, which would have potentially seismic implications for parliament.
ITV News Deputy Political Editor Chris Ship reports:
Prime Minister David Cameron has called Alex Salmond "a politician of huge talent and passion" after the First Minister announced he was stepping down.
He has been an effective First Minister and always fights his corner.
While we disagree profoundly about his goal of a separated Scotland, and many other things, I respect and admire his huge contribution to politics and public life.
David Cameron said he was "delighted" Scotland had voted to remain in the UK and that it was time for the UK "to come together and move forward".
Just one in three Brits think David Cameron should resign as Prime Minister if Scotland becomes independent, the latest ComRes/ITV News Index poll shows.
Of those surveyed, 31% agreed Cameron should resign if Scotland votes Yes at the referendum.
Almost half (48%) said he should not give up his post as Prime Minister, while 21% said they did not know.
What happens after the Scottish referendum? There will be changes no matter what the outcome.Read the full story ›
David Cameron has spoken to European leaders and agreed to push ahead with Russian sanctions by the end of the week, his spokesman has confirmed.
- ITV News' Political Editor Tom Bradby reports:
The Prime Minister gave a strangely anti-politics speech. In a way, he was effectively saying "look at all the things we've done together as people: standing in the trenches, defeating fascism and all the rest of it."
He has been criticised throughout for not showing enough emotion. I think everyone this week has woken up to the fact that independence is a real possibility, including the Prime Minister, and he is a bit desperate.
I think part of that desperation is about emotion. I don't doubt that he personally cares a lot about the union and would be devastated if it split up.
The Prime Minister has said he cares "far more about his country than his party", as he visits Scotland in a bid to increase support for the No campaign ahead of the referendum.
During a visit to the Scottish Widows offices in Edinburgh, David Cameron said: "I care hugely about this extraordinary country, this United Kingdom that we've built together. I would be heartbroken if this family of nations that we've put together was torn apart."
He added it was important to "talk about what we care about and how we feel about this amazing country, the United Kingdom, that we've built together."
The Prime Minister has declined to give a timetable for the removal of the Trident nuclear weapons system, which is based in Scotland, defending what he called the "ultimate insurance policy".
He said that the UK was safer because of its strong armed forces, and that he would not leave Britain "subject to blackmail by other countries that have nuclear weapons".
The Prime Minister has said there is "very wide agreement" between the pro-union parties on the issue of devolution.
He said there was "very clear political will among the parties and that's as close to a guarantee [of devolution] as you can get".