The space agency said there was a "lot of excitement" over the plans.
"NASA is opening the International Space Station to commercial opportunities and marketing these opportunities as we've never done before," NASA chief financial officer Jeff DeWit said in New York.
Officials added that they were keen to have the private sector become more involved in space, including the "development of products useful on Earth."
Why is NASA doing this? At the presentation Friday, NASA said it wasn't looking to make a profit from the trips, but the money raised would help towards achieving long-term goals. These include returning humans to the moon by 2024 and even sending them to Mars after that.
How will passengers qualify?
As well as stumping up the cash, the dozen or so private astronauts will have to meet the same medical standards and training and certification procedures as regular crew members. SpaceX and Boeing will choose the clients and deliver them to the ISS via their own rocket-and-capsule launch systems.
What is the ISS? The space station orbits around 400 kilometers above the Earth. It is run by five space agencies with 15 countries involved. The first segment was launched in 1998 from Russia. Since 2000, it has been staffed by a crew of between three and six astronauts.