Two American agencies have been awarded licences but new US adoptions will be limited to children over the age of five, sibling groups and those with special needs, the US State Department said.
Americans have been unable to adopt from Vietnam since a 2008 ban imposed due to US embassy concerns that many adoptees had been trafficked or given up after their families were coerced.
Vietnam denied these claims but agreed to suspend adoptions with the United States.
"The United States welcomes Vietnam's efforts to enhance its child welfare and inter country adoption system," the State Department said.
More From This Section
It named Dillon International and Holt International Children's Services as the American agencies newly authorised to facilitate adoptions in Vietnam.
Nguyen Van Binh, director of the international adoption department at Vietnam's Ministry of Justice, confirmed it had granted licences to the firms.
There are now a total of 36 foreign adoption agencies operating in Vietnam, he told AFP, from countries including France, Italy and Sweden.
Tad Kincaid, founder of Ho Chi Minh City-based Orphan Impact, welcomed the restarting of adoptions with new restrictions as "a good step".
"It makes sense to focus on children who are hardest to place, as they are most likely to spend their entire childhood in an orphanage," he told AFP.
The lifting of the US-Vietnam adoptions ban comes as the former wartime foes move closer together, with a string of recent high-level visits, talk of ending a ban on sales of lethal weapons in place due to human rights concerns and greater trade ties.
Estimates of the number of children in Vietnamese orphanages vary widely from around 143,000 to 1.5 million, Orphan Impact's Kincaid said.