A sphere of knowledge is a unified body or collection of knowledge regarding a specific subject, interest or otherwise area of expertise possessed by an individual.

For example, philately, geology and zoology are all spheres of knowledge; so too are specific sub-divisions within these collections of knowledge. Thus, petrology, palaeontology, mineralogy, stratigraphy, tectonics, geophysics and geochemistry are all spheres of knowledge within geology, for example.