In natural habitats, animals receive many stimuli that vary in place and time. In such habitats, they can express a wide range of behaviours that define the species’ “behavioural repertoire”. Farming or captive environments are designed to meet their basic biological needs (e.g. for rest, feeding), but are far less complex than natural habitats. Animals thus may not be able to express some of the behaviours from their repertoire and as a consequence experience boredom. The concept of environmental enrichment refers to a wide range of modifications to the environment of captive or farmed animals that offer adequate stimulation and facilitate the expression of highly motivated behaviour, thereby promoting positive emotions and improving animal welfare. Environmental enrichment can be divided into five (non-exclusive) categories: relational, feeding, occupational, physical and sensory enrichments. A good knowledge of the behaviour and the biology of the species is essential for the design of relevant enrichments. The benefits and drawbacks of enrichments need to be assessed in both short and long term by studying the use of enrichments in terms of occupancy value, the preference and motivation of animals to use them and the impact on welfare. To support positive animal welfare, high quality enrichment that engages animals over a long period of time should be seriously considered.