Needless to say, astronauts need to have expert knowledge of science and technology. In addition, they are required to be fluent in English, in order to communicate with astronauts from different countries who live and work with them. Astronauts have been selected based on the screening of application documents; a series of written exams on the English language, general and specialized knowledge of natural science, interviews, and medical and psychological examinations.

After being selected, astronaut candidates undergo Basic Training. They obtain basic knowledge and technical skills in space engineering, space science, space medicine, the Space Shuttle and ISS systems, the English and Russian languages. They also receive flight training and physical training. Upon completion of Basic Training, they are officially certified as astronauts and receive more advanced training in the operation of spacecraft systems and experimental equipment, as well as training to work in space. They also continue with language instruction, flight training, and physical training.
After assignment to a specific ISS mission, astronauts receive training in the specific tasks to be conducted during launch, in orbit, and on return, and participate in simulation training along with other astronauts and flight controllers.
So far, those training sessions have been conducted mainly by NASA;
but for participation in the ISS, Japanese astronauts, training sessions will be conducted mainly at JAXA.