Animal shelters, pounds and rescue organisations have evolved over time. Today they serve three purposes: to reduce animal welfare harms, to reduce harms to the community associated with free-roaming, stray or unwanted companion animals, and to reduce their associated environmental harms. This discussion explores the evolution of animal shelters, and argues that they are justified on utilitarian grounds. It explores unintended harms of shelters on animal welfare, including humane killing for the purposes of population control and shelter population management, as well as risks associated with confinement including behavioural deterioration and infectious diseases. It also explores harms to non-human animals, including moral distress and compassion fatigue. Finally, it explores potential environmental harms of shelters. The One Welfare concept, utilised in the World Animal Health Organisation (OIE) Global Animal Welfare Strategy, acknowledges the interplay between animal welfare, human well-being and environmental sustainability. It is argued that the One Welfare framework is critical in minimising harms and maximising benefits associated with animal shelters.