Although paleoecology has roots in the observations of pre-Christian scholars, consciously paleoecological inquiry is barely more than 100 years old. Equally a part of paleontology and a unifying interdisciplinary department within the wider realms of geology, it now enjoys significant interplay over a broad range of advancing science. The objectives of paleoecology are to understand and to interpret in mutual interrelation, the life processes, sociology, behavior, habitat conditions, biogeography, and evolution of prehistoric organisms, communities, and biotas. Those aims can be achieved only in part by the indispensable methods of classical natural history. The scope and rate of progress depend also on the imaginative supplementation of such methods with the tools, liberating concepts, and data of geochemistry, sedimentology, oceanology, and climatology - under the cohesive principles of parallel and proportionate relationships, and in biological perspective. Paleoecologists need to differentiate between the ambient environment of once living organisms, the sedimentary environment, and the diagenetic environment, and to recognize and treat the complexity of each. Each of these realms involves a variety of interface relations, climatic effects, interactions between organic and inorganic components, dispersal mechanisms, and gradients of several sorts that can be either clarifying to the perceptive or confusing to the unprepared. Some fundamental problems that are interwoven with paleoecology include the origin of life, Precambrian evolution, biochemical and physiological evolution, the development of behavior, the nature and depth of sedimentary deposition, paleoclimatology, paleobiogeography, and the possible mechanisms and biogeochemical consequences of extinction. Summary discussion of these subjects underscores their complexity and their paleoecological significance.