It is the work that astronauts do outside the pressurized cabin with the purpose of conducting scientific experiments, or building structures in space.
To develop extra-vehicular activity special suits have been studied and manufactured that ensure the astronaut's body the atmosphere and pressure necessary to live and protect against harmful radiation, as well as propulsion systems, which allow the astronaut to perform movements in conditions absence of weight and friction in which it is found.
The first man to perform an extravehicular activity, thus paving the way for successive experiments, was Soviet astronaut Aleksei Leonov. On March 18, 1965, during the flight aboard Voskhod 2, he left the spacecraft and remained outside, held with an umbilical cord, for ten minutes.
Successive attempts were carried out by the American astronauts of the Gemini project. Long and fruitful has been the extra-vehicular activity carried out by the Apollo astronauts on the lunar surface. Today it has become almost routine.