South Downs National Park Authority now fully operational
1 April 2011 Last updated at 20:27 BST
Campaigners have welcomed a "historic day" as the South Downs National Park Authority comes into full operation.
The authority has taken on its legal powers and will be responsible for all planning within the park.
The park, which covers 627 square miles across Sussex and Hampshire, was approved on 31 March 2009 and was officially designated a year later.
Jeremy Cooke reports.