“Tacit” knowledge is an important point in knowledge management: the question is the possibility to make it explicit. Many researches in economics or management underline that it is a very high stake. We focus specially on individual knowledge. Following Polanyi’s work, we substitute the notion of “knowing-in-action” defined by Piaget for the notion of “tacit knowledge”. The “tacit” dimension is one feature of this knowledge; it suggests a particular level of consciousness: a pre-reflective one. Unlike a sociological interview, some methods allow us to approach this kind of knowledge, to help the actor to make it explicit and to formalize it.