Ashraf Ghani has been inaugurated as Afghanistan's new president and has sworn in Abdullah Abdullah as chief executive.
The two men took their oaths of office in Kabul on September 29 in Afghanistan's first-ever democratic transfer of power.
Outgoing President Hamid Karzai had been Afghanistan's only leader since 2001.
"In the name of God the most gracious and most merciful," Ghani said in an oath administered by the chief justice, "I swear in the name of God that I will follow and support the holy religion of Islam, observe the constitution and all laws and remain vigilant for its application, guard the independence, national sovereignty, and territorial integrity of Afghanistan and protect the rights and interests of the people of Afghanistan."
For his part, Karzai spoke of the challenges he confronted during his 13 years in office.
"Thirteen years ago I began my journey with my honorable nation. It wasn't an easy journey. There were a lot of thorns on the way and brutal storms," Karzai said. "My mission was to take the delicate and thin goblet of the country safe to its destination."
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Ghani was officially declared the winner of the presidential election on September 21, some three months after the second round of the election was conducted.
He has pledged to sign an agreement with the United States to allow about 10,000 American troops to stay in the country after the international combat mission ends on December 31.
Abdullah, as chief executive, will have a new role similar to a prime minister in a government structure far different to Karzai's all-powerful presidency.
Afghanistan's democratic transfer of power was plagued by accusations of electoral violations from both Ghani and Abdullah, both of whom claimed to have won the June 14 election.
Under heavy pressure from the United States and UN, the two candidates eventually agreed to form a "national unity government." Ghani was declared president after an audit of nearly 8 million ballot papers.
An Afghan policeman stands guard at the site of a deadly suicide attack in Kabul on September 29.
John Podesta, counselor to President Barack Obama, led a 10-strong U.S. delegation, with President Mamnoon Hussain representing Pakistan and Vice President Hamid Ansari traveling from India.
Many other countries, including Britain and France, were represented only by their ambassadors in Kabul, while China sent Yin Weimin, minister of human resources.
In his inaugural speech, Ghani said his priority is to bring peace to the country.
"We ask opponents of the government, especially the Taliban and Hezb-e-Islami, to enter political talks," Ghani said after being sworn in. "Any problems that they have, they should tell us. We will find a solution."
Ghani also thanked Abdullah for his cooperation in the power-sharing deal.
"The national unity government is what Afghanistan needs. A national unity government doesn't mean division of power. It means dividing the jobs and responsibilities for serving people," Ghani said. "This government will represent the will, desire, and aspiration of Afghan people. I would like to thank my dear brother Abdullah Abdullah who through his cooperation and participation brought this process to a successful end."
In early international reaction to Ghani's inauguration, Swedish Foreign Minister Carl Bildt tweeted on September 29: "First ever peaceful and democratic transition of power in Afghanistan. Hugely important. And encouraging."
On inauguration day, two bomb attacks took place on the road connecting the country's main airport with the palace.
One roadside bomb did not result in any deaths or injuries, but a second attack about a kilometer from the airport by a suicide bomber killed at least four civilians, police said.
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Both Ghani and Abdullah are moderate, pro-Western leaders who have vowed to push ahead with the patchy social and infrastructure progress made since 2001, but the country still faces a major threat from Taliban militants.
Large-scale insurgent offensives have been launched in several provinces in recent months, with the Afghan Army and police struggling to recapture lost ground.
NATO operations have been scaled back rapidly and its combat mission will finish at the end of this year.