At the present time, it has been clearly demonstrated that at home oxygen therapy either on a long term basis or on a continuous basis brings important benefits for a patient: his/her physical and neuro-psychological conditions improve and his/her quality of life increases. However, given that this is some controversy about its indications, therapeutic effects and manner to administrate it, the authors review all these aspects, drawing from very up-to-date bibliographical references. At a later date, in another article, these same authors will evaluate nursing treatment corresponding directly to at home oxygen therapy.