This volume presents the results of an analysis of microscopic wear traces on chert artefacts from a variety of pre-ceramic period sites in Colombia. Nieuwenhuis uses trace-wear analysis to explore the relationship between Abrian and Tequendamian artefacts, and the different systems of tool production and use. Focusing on material from sites in the high plain of Bogotá and the middle Magdalena Valley, Nieuwenhuis extends the study to consider the complex relationships between tool use and changes in climate and environment, and argues that the traditional chronological division between the two classes of artefact is no longer valid.