This volume features an update of the 2017 review on natural product molecular fossils. The chapters survey the remarkable progress achieved since this earlier assessment in identifying, interpreting, and reinterpreting the chemical remnants of ancient life preserved in sediments, rocks, amber, fossils, and archaeological materials. It covers the full chemical spectrum of molecular fossils, from simple hydrocarbons and pigments to polymers, alkaloids, nucleic acids, and intact metabolites and documents how advanced analytical methods, including high-resolution and tandem mass spectrometry, compound-specific isotope analysis, synchrotron-based techniques, and machine learning, have transformed the field. Emerging disciplines such as paleometabolomics, paleoproteomics, and the search for extraterrestrial organic compounds are treated alongside classical biomarker geochemistry. Throughout, the chapters emphasize that reliable interpretation demands rigorous contamination controls, critical evaluation of biological source assignments, and the integration of chemical, geological, and paleobiological evidence. It is hoped that this contribution will be of broad interest to organic chemists, geochemists, paleontologists, astrobiologists, and archaeologists.