Kenya has a new constitution that makes significant changes in the way the country is governed.
The document was signed into law by President Mwai Kibaki at a ceremony in Nairobi.
The BBC reports the constitution is expected to bring significant changes. Some have billed it as the most important political event in Kenya's history since it gained independence from Britain in 1963.
The new constitution will bring a more decentralised political system, which will limit the president's powers and replace corrupt provincial governments with local counties.
It will also create a second chamber of parliament - the Senate - and set up a land commission.
The previous constitution allowed politicians to exploit tribal divisions, left courts weak and concentrated power in the president's hands.
Among those at the ceremony was the Sudanese President Omar al-Bashir who has been indicted for war crimes by the International Criminal Court.
The International Criminal Court has reported his visit to the United Nations Security Council.