Abstract: ‘Social competence’ refers to the ability of an individual to optimise its social behaviour depending on available social information. Although such ability will enhance social interactions and thus raise Darwinian fitness, its evolutionary and ecological significance has been largely ignored. Social competence is based on behavioural flexibility. We propose that the study of social competence requires an integrative approach that aims to understand how the brain translates social information into flexible behavioural responses, how flexibility might be constrained by the developmental history of an individual or by trade-offs with other (ecological) competences, and how social plasticity feeds back on fitness. Finally we propose a hypothesis of how social competence can become a driver of social evolution. Behavioural flexibility as phenotypic plasticity Adaptation to the environment is a universal characteristic of living systems. According to classic evolutionary theory, adaptation by natural selection relies on heritable phenotypic variation produced by genetic variation. However, when the rate of genetic evolutionary change is outpaced by changes in the environment the need for adaptive change without genetic mutation emerges [1]. In this scenario, the evolution of phenotypic plasticity is favoured, that is, a certain genotype produces different phenotypes depending on environmental conditions [2]. Among animals, behavioural traits exhibit a greater plasticity than morphological and physiological traits and plastic changes are reversible within an individual’s lifetime (‘behavioural flexibility’). This makes behavioural flexibility a powerful, immediate mechanism allowing organisms to adapt to changing environmental conditions, which may or may not be followed by other flexible adjustments of physiology or morphology. Many of these responses are simple reflexes and fixed action patterns elicited by a stimulus in the environment, when it deterministically predicts an appropriate response. However, when environmental complexity and variability increase, the capacity to adaptively modify behaviour as a function of experience and context is needed. Although some degree of context-dependent behavioural flexibility may be achieved with genetically determined rules, behavioural flexibility will often depend on cognitive abilities (understood as the acquisition, retention, and use of information; [3]) that allow individuals to adapt behavioural output to specific situations in a complex and variable world (e.g., see [4]). Interestingly, the evolutionary study of behavioural flexibility has rarely been framed within the scope of phenotypic plasticity, but rather in terms of cognitive evolution and ecology [3,5]. This is most probably due to the fact that in contrast to morphological and life history traits (which have been the main focus of phenotypic plasticity studies, and whose plasticity results from processes during development and is usually non-reversible) behavioural flexibility involves rapid changes, is labile, and is present during the whole life of the animal [6,7].