Launching Labour's campaign north of the border with Scottish party leader Iain Gray, Scottish Secretary Jim Murphy declared: "This is game on and we are going to fight from now until 10pm on polling day to re-elect Labour and stop the Tories winning back power. "The choice over the coming days will determine the future of Scotland for years to come.
"We want to secure Scotland's economic recovery and give people the chances they need and get on in life.
"The Tories aren't interested in this; they've shown time and again that they haven't changed and don't understand Scotland."
Scottish Tory leader Annabel Goldie said she was "confident" the party, which had one Scottish MP in the last parliament, could win seats across Scotland.
She said: "The choice is clear - five more years of Labour waste, Labour debt and Labour tax or a fresh start and change with David Cameron's Conservatives.
"The Conservatives have the ideas and policies to help people. Labour on the other hand have simply run out of ideas and are set to run a negative campaign.
Wider economy including tax
Abortion and embryology
"I am confident the Conservatives can win seats right across Scotland. People know that if they want change then the only way of achieving it is by voting Conservative. Scotland has a role to play in bringing about change and every vote, every constituency, every Conservative MP is crucial. Scotland can be part of it."
SNP leader and Scottish First Minister, Alex Salmond, called on voters to back "SNP champions" to provide a strong Scottish voice amid the "discredited" Westminster system.
He said: "The London parties offer the same agenda - they are part of the same metropolitan, political machine.
"The London parties have blown the gaff on their plans for Scotland - by their own admission, Labour would cut 'tougher and deeper' than Thatcher, and the Tories are planning a special cut for Scotland despite being funded by Scottish resources, blowing their respect agenda away.
"The SNP are going into this campaign with a clear message for Scottish voters - more votes means more Nats, and more Nats means less cuts."
The Liberal Democrats are fighting the campaign on a pledge for fairer taxes, a fairer start for children and a greener economy.
The party's Scottish leader Tavish Scott said he was "thrilled" to be starting the campaign, saying the contest in many Scottish seats were a straight fight between the Lib Dems and Labour.
"The Tories only have one MP in Scotland and it will be the Liberal Democrats who make Scotland a Tory free zone," said Mr Scott.
Meanwhile, former Scottish Green leader Robin Harper called on the parties to fight a "clean" campaign by refraining from personal attacks and only making "honest and reasonable" pledges.
The MSP, who is fighting the Edinburgh East seat, added: "Voters are tired of negative campaigning, of insults and innuendo - Greens across Scotland will continue to campaign on the issues that matter to local people, including the economy, health, education and climate change."
The 2005 UK election saw Labour emerge in Scotland with 41 MPs, including the seat held by the then Commons speaker, Michael Martin.
The Liberal Democrats won 11 seats in the poll, which saw the introduction of new constituency boundaries, while the SNP had six and the Conservatives won one seat.
Several Scottish seats have changed hands since 2005, following a series of by-elections, including the Lib Dems winning the Dunfermline and West Fife seat from Labour in 2006.
The SNP also won Glasgow East from Labour in 2008, while Labour came first in last year's contest in the Glasgow North East constituency, after Mr Martin quit as Commons speaker and as an MP.
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