The use of the term "kerogen", originally described as the organic matter in oil shale, has been extended to include all nonsoluble solid organic matter in sedimentary rocks. Kerogen is divided into "types" based on elemental composition and potential maturation path. "Maceral" nomenclature, originally developed to describe the organic components of coal, has also been extended to source rocks and, later, oil shale. The extension and overlap of these two fields creates problems as attested to by the proliferation of vitrinite terminology and the application of the term vitrinite to organic matter that is not clearly derived from woody tissue. Other problems include the fundamental complex and wide-ranging nature of Type II kerogen which is now acknowledged to be a highly heterogeneous material. Present-day understanding of kerogen has exceeded the simple three- or fourfold division of kerogen, thus making the division (classification) outdated and deficient. Maceral terminology is based on the direct observation of the morphological and optical properties of the organic matter which ultimately reflects their internal chemistry. Problems associated with maceral terminology notwithstanding, the fundamental framework of organic matter in sedimentary rocks is best served by maceral nomenclature. This is consistent with observations that kerogen, or solid sedimentary organic matter, is clearly composed of macerals.