Emotions are a key factor to understanding behaviour and cognition. In fact, the way animals perceive and react to their physical and social world is critical for understanding the differences and similarities among individuals, populations and species. When considering social animals, emotional and social regulation, which can be measured through a variety of methods, sustain the appearance and maintenance of social behaviour, including maternal behaviour, affiliative and agonistic episodes and the social relationships between infants and the members of their group. For instance, by watching and coding the behaviour of wild capuchin monkeys, who show a slow development and an extended infancy, compared to other non-human primates, we can have a glance on how particular behaviours and individual differences affect the development of social bonds and interactions. In this talk, I will present the capuchin monkeys (extraordinary neotropical monkeys), their complex net of social relationships and how the study of emotional and social regulation can unravel much of the fascinating world of social animals.