Deputy First Minister Nicola Sturgeon has called on the pro-Union Better Together campaign to outline what a "no" vote in the referendum would mean for voters.
She said the Scottish government's White Paper on independence provided a "compelling case" and urged Better Together to offer an alternative vision for Scotland.
All three of the parties that make up Better Together have said they favour more devolution for Scotland.
But what exactly do they favour, and what have they said so far?
In early 2012, Labour leader Johann Lamont said: "Devolution is a process, not an event. I want the current devolved settlement to be renewed, refreshed and deepened."
In March of that year, the party set up a commission to look at the future development of devolution.
An interim report, titled Powers For a Purpose - Strengthening Devolution, was published in April 2013 and concluded that there was a case for income tax to be devolved to Holyrood. Under the plan, MSPs would decide the rates and bands of income tax depending on spending commitments.
But the commission, which includes MPs, MEPs, councillors, union members and academics as well as Ms Lamont, also reflected concern among some Labour MPs that full transfer of income tax was a step too far.
The report said it would not back any plan leading to cuts in Scotland's funding or an undermining of the Barnett Formula.
Under the plan, control of corporation tax, VAT, North Sea oil tax, benefits and pension and alcohol and tobacco duties would remain at Westminster.
The report rejected other possibilities, including fiscal autonomy, which it described as "a thinly disguised version of independence", but argued for a bigger role for local government in Scotland, including control of Crown Estate shoreline revenues.
The report also backed the devolution of vehicle excise and air passenger duties.
Drew Smith, Scottish Labour's constitutional spokesperson, said: "It was Labour who delivered the Scottish Parliament and played a key role in the ongoing enhancement of its powers through the Calman Commisson. We look forward to building on this proud record by bringing forward our proposals on strengthening devolution in the spring."
Scottish Liberal Democrats
The Liberal Democrats have long been proponents of home rule for Scotland within a federal Britain.
They set out their most recent plans in October 2012 with a report titled Federalism - the best future for Scotland, written by a constitutional commission chaired by former Liberal Democrat leader Sir Menzies Campbell, who has called the current arrangements "unsustainable".
As well as delivering home rule for Scotland - a system where the vast majority of domestic policy would be decided and managed by the Scottish Parliament - the report advocated significant devolution from Westminster for other parts of the UK, including England.
The report argued for "fiscal federalism", where Scotland would raise and spend most of its own taxes and borrow on its own terms. The Barnett Formula would be scrapped and replaced with a new "needs-based" arrangement reflecting the fiscal changes.
Oil would continue to be managed at a UK level, as would welfare and pensions, defence and foreign affairs.
Under the plans, the Act of Union between Scotland and England would be scrapped and replaced with a declaration of federalism.
Scottish Liberal Democrat leader Willie Rennie said: "With a consensus on more powers emerging the momentum is now behind our party's approach on new powers that should be delivered when Scotland opts to stay in the UK."
In March 2013, Scottish Tory leader Ruth Davidson set up a commission, headed by Lord Strathclyde, the former leader of the House of Lords, to look at further powers for the Scottish Parliament.
Announcing the commission, she said the party was "committed to a new path; more responsibility for the Scottish Parliament and a strengthening of devolution."
During her leadership campaign in 2011, however, Ms Davidson had described the current devolution settlement as "a line in the sand".
Although she set up the commission, which also includes former Tory leader Annabel Goldie, former presiding officer Alex Fergusson, business leaders and academics, Ms Davidson is not contributing to its work.
The commission will report later this year, according to the Scottish Conservatives, when Ms Davidson will consider its findings and announce the party's position on further devolution before the referendum on 18 September.
A Conservative spokesman said: "The Scottish Conservatives want devolution to work better for people in Scotland and that is why we set up the Strathclyde Commission, which will report back in good time before the referendum vote."