Minimum wage up to £5.93 an hour
The national minimum wage has risen to £5.93 an hour from £5.80 and for the first time people aged 21 will benefit from the rate.
Previously the full rate applied to employees aged 22 and older.
There are also corresponding increases for younger workers, with 16 and 17-year-olds seeing a rise from £3.57 an hour to £3.64.
For 18 to 20-year-olds the rate is increasing from £4.83 to £4.92 an hour, the new rules state.
The government has also introduced a minimum wage for apprentices for the first time, of £2.50 an hour, for those under 19 years old.
It will also apply to young workers aged 19 or over during the first year of their apprenticeship.
However, the British Retail Consortium (BRC) has warned the government about further rises that could damage job creation.
It said next year's increase must be no more than 1.7%, as a larger rise would seriously impede retailers' ability to maintain and create jobs.
Stephen Robertson, of the BRC, said the government must strike the right balance between higher wages and more jobs.
"Trading conditions are tough, higher costs, such as next April's National Insurance increase will pile on even more pressure," he said.
"Even a small increase in 2011's minimum wage could choke off retailers' vital potential to create new jobs."
The government is also cracking down on employers who flout the minimum wage laws. It said it would name and shame offenders, publicising breaches from 1 January 2011.
Employment Minister Edward Davey said firms had three months to put their house in order.
"Bad publicity can be a powerful weapon in the fight against employers who try to cheat their workers and competitors. Their reputation can be badly damaged if they are seen to be flouting the law," he said.
The national minimum wage was introduced in 1999, at a rate of £3.60 an hour.