The Proterozoic Biosphere is the first major study of the paleobiology of the Proterozoic Earth. It is a multidisciplinary work dealing with the evolution of the Earth, the environment, and life during the forty percent of Earth's history that extends from the middle of the Precambrian Eon (2500 Ma) to the beginning of the Paleozoic Era (550 Ma.). The Proterozoic Biosphere includes a vast amount of new data on Proterozoic organisms and their modern analogs. Prepared by the Precambrian Paleobiology Research Group, a multidisciplinary consortium of forty-one scientists from eight countries, this monograph will serve as a benchmark in the development of the science of the biochemistry and the organic chemistry of Proterozoic sediments. The three main goals of this study are: (1) to amass, evaluate, and synthesize the large body of paleobiologic data available from previous studies, eliminating mistakes so that future investigations will not be encumbered by them; (2) to generate new data and new analyses based on the reexamination of previous studies and on new investigations within an interdisciplinary framework; (3) to build toward the future by placing special emphasis on new or relatively neglected aspects of paleobiologic study and by highlighting major unsolved problems in the field.