It is the start of a long mission in space for a US astronaut and two Russian cosmonauts.
The three men blasted off in a Russian Soyuz rocket from the Baikonur Cosmodrome in Kazakhstan on Friday.
Their mission is on the International Space Station, where two of the men will stay for a year.
This is twice as long as previous crews.
The mission is a chance for scientists to see how humans cope in space for so long.
This is particularly important for any future planning of multi-year missions to Mars.