First Minister Nicola Sturgeon announced the full lockdown amid rising coronavirus cases, and a new variant.
It comes amid calls for a national lockdown in England with pressure mounting on Prime Minister Boris Johnson.
In today's (Monday) announcement, Nicola Sturgeon said she is more concerned about coronavirus now than she has been for the duration of the pandemic.
Updating MSPs in Holyrood, the First Minister announced a lockdown would be in effect in Scotland for the duration of January.
She said: "It is no exaggeration to say that I am more concerned about the situation we face now than I have been at any time since March last year."
NHS capacity is already beginning to strain at some health boards, the First Minister said, with NHS Ayrshire and Arran currently at 96% capacity, while Borders, Greater Glasgow and Clyde and Lanarkshire are above 60%.
Sturgeon told the Scottish parliament that from midnight people would face a legal requirement to stay at home except for essential purposes, similar to the lockdown imposed at the start of the pandemic in March last year.
"The situation ... is extremely serious," she said.
Schools will remain closed until at least February, for most pupils.
The First Minister told MSPs: "The advice of our clinical advisers is clear that the increased transmissibility of the new variant means that the current Level 4 measures may not be sufficient to bring the R number back below one.
"It is essential that we further limit interaction between different households to stem the spread and bring the situation back under control, while we vaccinate more people.
"In short, we must return for a period to a situation much closer to the lockdown of last March."
Speaking about the vaccination programme, the First Minister said more than 2.5 million people will receive either the AstraZeneca or Pfizer vaccine by the end of the spring.
She added: "Our current expectation, based on assumptions about supply and the new advice on doses being administered up to 12 weeks apart, rather than three, is that by early May everyone over 50, and people under 50 with specific underlying conditions, will have received at least the first dose of vaccine."
The First Minister also said that one million people will be vaccinated by the end of January.
Boris Johnson previously said he would act "in due course" and "will do everything that's necessary".
But he was warned not to delay the announcement of new restrictions in England as cases and pressure on the NHS increased.
The latest data show a 41% rise in the number of confirmed coronavirus patients in hospital in England between Christmas Day and January 3, figures which have caused alarm in Whitehall and the health service.
"If you look at the numbers there's no question we will have to take tougher measures and we will be announcing those in due course," Mr Johnson said during a visit to Chase Farm Hospital in north London.
With 78% of England's population already under the toughest current restrictions, ministers are examining how successful the Tier 4 measures - which came into force for the first time on December 20 - have been.