The first maps detailing the 'right to roam' on privately owned land are being published on Sunday.
The new freedoms mark a milestone in a decades-long battle
The Countryside Agency is printing open access maps for the whole of England over the next 15 months.
The first ones cover the south east and the lower north west, which includes the Peak District, and will be greeted eagerly by ramblers.
But some landowners are worried that incorrect areas will be included and that farmland will be damaged.
Any private land considered moor, heath, mountain or downland or registered common land will now be open to walkers.
Ramblers groups are jubilant and have called these maps the most exciting development since the creation of national parks after World War II.
But opponents say consultation has been scant, decisions on what constitutes open access land have been bizarre in some cases and the appeals process has been time-consuming and costly.
The new laws do not give people a right to roam anywhere. Areas like gardens and cultivated land are not included and there are restrictions on some areas at certain parts of year.
A total of 105,253 hectares of new access land will be opened on Sunday - 13,853 in south east England and 91,400 in the lower north west.
Other areas will then follow suit.
Walkers have turned out to mark the introduction of the Countryside and Rights of Way Act.
Nick Barrett, chief executive of the Ramblers Association, said: "This is a truly historic day. These landscapes are as much a part of our national heritage
as structures like Stonehenge.
"For many, the joy of walking is about getting off the beaten track - everybody in this country now has a right to do just that and I hope people will take the opportunity to discover these beautiful areas for themselves.
"I am confident the respect and love walkers have for the countryside will prove that this is a wise, fair and beneficial piece of legislation."
The success for ramblers comes after years of lobbying and direct action in an effort to get access.
Perhaps the most notable protest was the Kinder Scout mass trespass in Derbyshire in 1932 that saw ramblers in violent clashes with gamekeepers.
But one of the people not taking part in walks marking the start of the right to roam is the rural affairs minister, Alun Michael.
There were fears he would be targeted by protesters after a pro-hunt group warned the minister that the countryside was now a 'no-go' area for Labour in the wake of the hunting debate.
Mr Michael said he had withdrawn because he did not want to disrupt the celebrations, but denied the countryside had become a 'no-go' area for Labour ministers.
Mr Michael, the minister responsible for steering a hunting ban through Parliament, had been due to join walkers in the Forest of Bowland, Lancashire, on Saturday and at Derbyshire Bridge in the Peak District on Sunday.