It is critical that glacial scientists continue to refine their interpretations of ancient archives of subglacial processes, specifically those represented by tills and associated deposits, as they form the most widespread and accessible record of processes at the ice-bed interface. Unfortunately, despite a long history of investigation and a lexicon of process-based nomenclature, glacial sedimentologists have yet to reach a consensus on diagnostic criteria for identifying till genesis in the geological record. What should be called till? Based on the author’s extensive field research, as well as the latest literature on the subject, this book attempts to provide a definitive answer to that question. It critically reviews the global till literature and experimental and laboratory-based assessments of subglacial processes, as well as the theoretical constructs that have emerged from process sedimentology over the past century. Drawing on a wide range of knowledge bases, David Evans develops a more precise, contemporary till nomenclature and new investigatory strategies for understanding a critical aspect of glacial process sedimentology.