« Ethics and Economy: at the source of rationality » is a joint of the efficiency imperative and freedom when it is a question of acting « economically ». It is about the economic rationality concept evolution through the various coordination modes (the market, the hierarchy, the agreements, the standards (including the Ethical values) and rules). The Ethical dimension the basis of motivation joins in the rationality postulate evolution process giving rise to a new definition of value and to solidarity economy appearance a first stage of a progress leading towards a sustainable development.