French President Nicolas Sarkozy inaugurated the conference, which is being attended by delegates from more than 65 countries and 15 international organizations.
Afghan President Hamid Karzai asked participants to support a $50 billion, five-year plan to rebuild his country in the face of an ongoing insurgency.
Karzai said Afghanistan still needs large-scale support from the international community.
He also emphasized that the aid must be spent wisely in an apparent reference to donors' concerns that Afghan state structures cannot handle the aid they already have, let alone billions of dollars in new commitments.
Karzai also urged Afghanistan's neighbors to join with Kabul in fighting terror, saying the problem can only be tackled at regional level.
"The fight against international terrorism calls for a regional political commitment that is based on sincere partnership and cooperation, recognizing that the menace of terrorism is a threat to the entire region," Karzai said.
U.S. First Lady Laura Bush urged world donors not to turn their backs on Afghanistan, saying the country has reached "a decisive moment for its future." She confirmed that the United States is pledging $10 billion in aid to Afghanistan over the next two years.
Some other pledges of assistance were announced before the forum got under way. The World Bank said it would provide around $1.1 billion over five years, and Germany pledged $655 million.
However, the money raised at the conference is expected to fall well below the $50 billion total requirement set out by Karzai. Donor countries are worried about large sums of money being swallowed up by Afghanistan's pervasive corruption.
Diplomats noted that the conference would also seek ways to improve coordination on reconstruction projects among foreign nongovernmental organizations.
AP quoted Brad Adams, Asia director of the U.S.-based Human Rights Watch (HRW), as saying donors cannot simply offer money and ignore the need for systemic reform in Afghanistan.