Animals are killed in different circumstances for different reasons. Culling is used to describe the killing of animals or groups of animals to reduce or eliminate a population in a particular place. Euthanasia is derived from the Greek and means ‘a good death’. The evaluation of killing methods must consider the animals to be killed and the personnel involved. In general, the extent to which an animal’s death affects its welfare is estimated by the duration and severity of any adverse affective states that the animal experiences before the point at which it loses consciousness for the last time. After this point, the animal cannot experience anything. Methods for killing animals are of three types, and in each category, death is brought about by extreme and permanent alterations to either the structure and/or function of the central nervous system. Death may be caused by physical methods such as shooting, cervical dislocation and decapitation; by functional disruption of the central nervous system using methods that don’t physically destroy it, such as electrocution or chemical disruption; or by deprivation of oxygen required by the central nervous system, such as exsanguination, carbon monoxide inhalation and low atmospheric pressure stunning.