The chapter discusses how the field of paleoecology has evolved to become a crucial part of paleobiology. It highlights a shift towards focusing on the biological aspects of fossil organisms and comparing them to living species, rather than just the physical environment. This new approach draws heavily from theoretical ecology and biogeography, using mathematical models to understand community structure, colonization, extinction, and evolution. The integration of these disciplines has led to a more comprehensive understanding of ancient ecosystems and the organisms that inhabited them.