Scotland is to receive £2.5bn in infrastructure investment for so-called next-generation broadband, according to BT.
The communications firm announced its biggest "superfast" fibre-broadband project for Scotland, covering around 277,000 homes and businesses.
BT said the Openreach project has a mix of "fibre to the cabinet" (FTTC) and "fibre to the premises" (FTTP) technology.
FTTC is delivered to "street cabinets" and claims download speeds as fast as 40Mbps. Openreach said it will roughly double these speeds next year.
FTTP goes directly into homes and business premises and claims speeds of up to 100Mbps, with the firm saying its project aims to treble this speed by spring.
However, research carried out by watchdog Ofcom in July showed the average broadband speed in the UK is just 6.8Mbps. BT said the number of homes and businesses able to access the superfast network will reach 685,000.
The 2012 upgrades cover 34 exchange areas including Aberdeen, Dundee, Edinburgh and Glasgow. The firm said smaller towns will also get access to the new network.
BT Scotland director Brendan Dick said: "It marks a major investment in infrastructure, which will give the country a tremendous boost. Next-generation broadband is essential for our nation's economic growth, so it's brilliant to be ending 2011 on such a high note.
"Superfast broadband will be welcomed by families throughout these 34 areas because it will help improve their quality of life and leisure and open new doors through online learning and fast access to information and services. And it's also going to provide a huge fillip (stimulus) for businesses.
"At a stroke, small and medium-sized firms will have access to big-business speeds at much lower costs, allowing them to find new markets, boost their competitiveness and create new jobs."
Infrastructure and Capital Investment Secretary Alex Neil said: "This is more great news for Scottish businesses and households across the country. Access to superfast broadband will help existing business expand, attract new business and will connect communities.
"We have set out our ambition for all of Scotland to have access to next-generation broadband by 2020, with significant progress to be made by 2015. It is an important part of the Scottish Government's economic strategy.
"The majority of investment in next-generation broadband should be led by the private sector and I welcome BT's plans to extend their superfast network further across Scotland."