Tacit knowledge is a philosophical concept first articulated by Michael Polanyi, who wrote, “We can know more than we can tell.” It is defined as the underlying or unspoken knowledge that guides people's actions and thoughts but that they may not be able to access consciously. It differs from explicit or focal knowledge. Different types exist, including expert knowledge, language competence, and basic ideas we use for everyday tasks. In organization development, tacit knowledge is a metaphor for the undocumented expertise that may be essential to guiding activities but is not written down and perhaps not even expressed.