Much of what we know we cannot say. And much of what we do we cannot describe. For example, how do we know how to ride a bike when we can't explain how we do it? These abilities, which we are unable to articulate, were labeled "tacit knowledge" by chemist and philosopher Michael Polanyi, but here Harry Collins analyzes the term, and the behavior, in much greater detail, often departing from Polanyi's treatment. In "Tacit and Explicit Knowledge", Collins develops a common conceptual language to bridge the concept's disparate domains by explaining explicit knowledge and classifying tacit knowledge. Collins then teases apart the three very different meanings, which, until now, all fell under the umbrella of Polanyi's term: relational tacit knowledge (things we could describe in principle if we put in the effort), somatic tacit knowledge (things our bodies can do but we cannot describe, like balancing on a bike), and collective tacit knowledge (knowledge we draw on that is the property of society, such as the rules for language).Thus, bicycle riding consists of some somatic tacit knowledge and some collective tacit knowledge, such as the knowledge that allows us to navigate in traffic. The intermixing of the three kinds of tacit knowledge has led to confusion in the past; Collins' book unravels these complexities and thus enables us to make new and better use of the underlying concept.