President Bush said he will miss Mr. Blair, calling him a political thinker who keeps his word. Mr. Bush indicated that he believes Mr. Blair's likely successor, Finance Minister Gordon Brown, will not change British policy on Iraq.
Many British political analysts say the unpopularity of the war in Iraq at home was a major reason for Mr. Blair's decision to quit.
European Commission President Jose Manuel Barroso praised Mr. Blair for what he said was bringing Britain from the fringes to the mainstream of the European Union.
Japan's Prime Minister Shinzo Abe said Mr. Blair achieved much in the past 10 years, especially in the economy and education.
But a senior Zimbabwean government official, Deputy Information Minister Bright Matonga, called Mr. Blair "the worst thing that ever happened to Africa."
Mr. Blair will step down as Labor Party leader and Prime Minister on June 27th after 10 years in office.
Mr. Blair is credited with revitalizing the economy and working to bring a power-sharing government and peace to Northern Ireland.
A poll in Thursday's edition of The Guardian newspaper shows that 44 percent of British voters think Mr. Blair has been good for Britain.
Mr. Blair agreed last year to step down early after a Labor Party revolt. A number of party members resigned to protest his Iraq policies and sagging popularity.
Associates of Mr. Blair say he will remain a member of parliament until the next national election, unless he receives a major international position.
Some information for this report provided by AP, AFP and Reuters.