Trust and trustworthiness are key elements, both at the micro and macro level, in sustaining the working of modern economies and their institutions. However, despite its centrality, trust continues to be considered as a “conceptual bumblebee”, it works in practice but not in theory. In particular, its behavioural rationale still represents a puzzle for traditional rational choice theory and game theory. In this paper “trust responsiveness”, an alternative explanatory principle that can account for trustful and trustworthy behaviour, is proposed. Such principle assumes that people can be motivated to behave trustworthily by trustful actions. The paper discusses the philosophical roots, the historical development, as well as the relational nature of this principle as well as its theoretical implications.