Now considered as a global "epidemic" by the World Health Organization (WHO), obesity is placed at the extreme end of the malnutrition continuum and affects almost all populations. The most frequently cited cause of obesity is a disturbance in the energy balance resulting from too much energy intake coupled with insufficient energy expenditure (i.e. a positive energy balance). The reasons for this imbalance are many and varied, which makes obesity a pathology with multifactorial origins, constituting a challenge for public health policies and for practitioners. The new knowledge on the socio-economic, psychological and environmental factors of obesity reviewed in this article provides the basis for new approaches to prevent and reduce the high prevalence of obesity.