More than 60 billion of broilers are reared and slaughtered for meat production yearly. The majority of broilers worldwide is housed indoors in floor systems and is of a fast-growing breed. Welfare problems have been associated with their efficient growth, the rearing environment and flock management. Examples are impaired leg health and behavioural restriction (the inability to perform their species-specific behaviour). Breed (fast- or slow-growing), hatching environment, stocking density, light, litter, air quality and environmental enrichment all affect broiler welfare, although their interactive effects are often unclear. Prevalence of welfare problems is generally lower in ‘higher-welfare’ systems, involving a slower growing broiler strain, lower stocking density and environmental enrichment. There seems to be a trend towards implementation of these higher-welfare systems in Europe and the US, although there is currently little information on needs and preferences of slower-growing strains and welfare of broilers in different production systems.