Housing systems for captive animals have often been designed on the basis of economic and ergonomic considerations, such as equipment, costs, space, workload, ability to observe the animals and to maintain a certain degree of hygiene, with little or no consideration for animal welfare. Environmental refinement can be defined as any modification in the environment of captive animals that seeks to enhance the physical and psychological well-being of the animals by providing stimuli which meet the animals’ species-specific needs. This article provides an overview of environmental factors that influence the well-being of captive animals with specific reference to the needs of the most common laboratory species.