Cognitive capacities refer to all mental processes such as attention, memorization, learning and reasoning skills. These cognitive capacities allow animals to understand and adapt to their environment, and are the basis of multiple behaviours. In this review, we first briefly present an overview of current knowledge on the cognitive capacities of poultry, with a focus on laying hens and broilers. We show that these birds have a diverse sensory world, develop rich social interactions and are capable of learning, among other capacities. Although more research is needed, these birds have a much broader repertoire of cognitive capacities than is often assumed. In a second part, we illustrate how this knowledge brings a new vision to the understanding of behaviours observed in farming systems, such as range use of free-range chickens, or injurious pecking in laying hens. The study of animal cognition, which is developing rapidly on the international level, contributes to a better understanding of the biology of these animals. In the long term, this research could lead to the development of original approaches to better orientate husbandry practices and to improve animal welfare.