Abstract Cherts, shales, and carbonates containing small amounts of organic matter occur throughout the Precambrian sedimentary record. The oldest known organic-rich sediments have been dated at > 3,000 million years. Knowledge of the composition, origin, and fate of the organic content of these rocks relates to many facets of Precambrian earth history. Apart from its primary paleobiological significance, organic geochemical research is also concerned with problems in atmospheric and hydrospheric evolution, sedimentation, diagenesis, metamorphism, and ore genesis. Precambrian organic geochemistry to date has rested on the premise that ancient life process can be profitably studied at a chemical level, as well as by examination of the morphological fossils of conventional paleontology. A decade of intensive research on selected Precambrian carbonaceous and bituminous sediments has been made possible by the refinement of analytical techniques (notably gas chromatography and mass spectrometry) which are now capable of detecting and characterizing the minute quantities of complex organic mixtures found in geological materials. It has resulted in the development of criteria which allow discrimination between indigenous and adventitious organic matter. A diverse array of stable organic compounds has been isolated from Precambrian sedimentary rocks. The compounds, termed chemical fossils, are thought to be derived from ancestral microorganisms and as such have contributed to the formulation of the biological marker concept. Despite reports of possible abiotic occurrences, a biological origin for most of the organic matter preserved in Precambrian rocks (whether sedimentary or metamorphic) now appears likely. The possibility of secondary emplacement from migrating formation fluids means that an indigenous chemical fossil need not have been syngenetic with the deposition of its host sediment. No conclusive test of Precambrian age as yet exists for these compounds. The bulk of the organic material (kerogen) in Precambrian rocks is insoluble in organic and aqueous solvents. For this reason, kerogen is almost certainly both indigenous and syngenetic, but clarification of its chemical structure must await the development of new analytical procedures. The nature and extent of the modification that the soluble and insoluble organic fractions have undergone during late diagenesis and incipient metamorphism is still virtually unknown. Correlation of chemical fossils with specific biogenic precursor compounds, or a particular type of primitive organism, therefore remains equivocal. So also comparison of the organic geochemical facies of one sediment with that of another may be complicated by differences in their thermal history and mineralogy. Recent interest in the possible involvement of living and decayed microorganisms in the genesis of certain Precambrian Fe, U, Au, Cu, Pb, and Zn metal deposits signals the beginning of an important new phase in organic geochemical studies.