Chapter 4 provides an overview of stable isotope analysis, with a specific focus on carbon, nitrogen, oxygen, and strontium, and outlines the pathways through which isotopes become part of human skeletal and dental tissues. Prowse also discusses how isotopes serve as tools for investigating diet, mobility, or geographic origins in the Roman world and notes limitations to such analyses. The author then provides an overview of major trends in Roman period isotopic analyses of diet, mobility, and geographic origins. The chapter concludes with the author’s suggestions for improvements in the field, including the need for better baseline data for isotope studies, further development of compound-specific approaches, and collaborations between bioarchaeologists, zooarchaeologists, and archaeobotanists.