Book excerpt: This book presents a series of review articles on nine important ancient orogens on Earth. Comparison of these mountain belts provides a wealth of information for the debate on whether there has been a change in mountain-building processes through the history of the Earth. As a precursor to these papers, the rheology of the Earth's lithosphere through time is reviewed. Theoretical analysis and insight into the behaviour of the lithosphere of other planets constrain mechanical considerations of the Earth's lithosphere. It is clear from these overviews that geodynamic concepts and modelling, and new techniques such as deep seismic profiling and geochronology are having a profound impact on orogenic studies.