In this presentation, the concept of trust and fairness is discussed from a developmental perspective. Trust and fairness have deep roots in development with early implicit signs expressed from the first weeks of life. Their development is considered here in parallel with the development of a conceptual and explicit sense of self emerging by the end of the second year. This development is prolonged with the universal emergence of instrumental inequity aversion between 3 and 5 years. Cross-cultural studies are presented suggesting that across highly contrasted cultures, a significant majority of 5 year-old children manifest such ethical stance. The general features of what appears to be a universal development toward trust, fairness, and overall equity between 3 and 5 years is discussed in relation to the self in development, and in particular in relation to children’s growing concerns about their own reputation. This development is interpreted as expression of the constraint of reciprocity and cooperation attached to the particularly high human dependence on others and the demands placed on children from any culture, regardless of their family’s social and economic status, to reciprocate as they adjust to group living outside of the family.