NASA has given SpaceX and Blue Origin the nod to develop its new lunar landers which will take the first woman and the next man to the surface of the moon.
The private spaceflight companies, owned by Elon Musk and Jeff Bezos, will develop competing systems in parallel, alongside a third company called Dynetics, but NASA will eventually choose one.
NASA has awarded the three companies 10-month contracts that are worth a combined $967m (£770m), with payments subject to the companies reaching specific development milestones.
The contracts are to design and build the human landing systems for NASA's return to the moon by 2024, including the launch and landing vehicles.
The SpaceX Super Heavy rocket, Blue Origin New Glenn Rocket System and the Dynetics Human Landing System are yet to be built or tested.
The three companies will spend the next 10 months refining their lander concepts alongside NASA until the space agency makes a decision about who to continue working with in February next year.
At that point, the agency will decide who can perform initial demonstration missions, and eventually who will be part of returning mankind to the moon.
NASA's new Artemis programme, named after the mythological sister of Apollo, the first moon mission's namesake, will lay the groundwork for an eventual manned mission to Mars.
"With these contract awards, America is moving forward with the final step needed to land astronauts on the moon by 2024, including the incredible moment when we will see the first woman set foot on the lunar surface," said NASA administrator Jim Bridenstine.
"This is the first time since the Apollo era that NASA has direct funding for a human landing system, and now we have companies on contract to do the work for the Artemis program."
Elon Musk, who is currently complaining about coronavirus lockdown measures, previously suggested SpaceX could potentially just fly to the moon itself if NASA wasn't willing to partner with it.
He claimed it would be easier for his company to actually land on the moon than try to convince the space agency and other authorities that it was up to the task.
"I want to say that it's important that this agency do this now, because our country, and in fact the whole world has been shaken by this coronavirus pandemic," Mr Bridenstine said.
"And yet, we need to give people hope. We need to give them something that they can look up to, dream about, something that will inspire not just the nation but the entire world."
