In medical practice, the different scenarios in which cardio respiratory resuscitation (CPR) may be applied must be taken into account. CPR is crucial in subjects that arrive in emergency rooms or suffer a cardiac arrest in public places or at their homes. It is also critical in hospitalized patients with potentially reversible diseases, who suffer cardiac arrest as an unexpected event during their evolution. In intensive care units, the decision is particularly complex. The concepts of therapeutic proportionality, treatment futility and therapeutic tenacity can help physicians in their decision making about when CPR is technically and morally mandatory. The do not resuscitate (DNR) decision in taken when a patient is bearing an irreversible disease and his life is coming to an end. DNR decisions are clearly indicated in intensive care units to limit the therapeutic effort and in other hospital facilities, when death is foreseeable and therapeutic tenacity must be avoided. DNR orders must be renewed and reconsidered on a daily basis. It does not mean that other treatment should be discontinued and by no means should the patient be abandoned. DNR and previous directives, DNR and quality of life and DNR communication are also commented in the present article.