The nature and tectonic significance of fault zone weakening: an introduction • Insights from neotectonic settings, deformation experiments and modelling studies • Implications of earthquake focal mechanisms for the frictional strength of the San Andreas fault system • Permeability variation across an active low-angle detachment, western Woodlark Basin (ODP Leg 180) and its implication for fault activation • Experimental constraints on the mechanical and hydraulic properties of deformation bands in porous sandstones: a review • Thermo-rheologic controls on deformation within oceanic transforms • Insights from natural fault rocks Clay mineral transformations and weakening mechanisms along the Alpine Fault, New Zealand • Deformation microfabrics of clay gouge, Lewis Thrust, Canada: a case for fault weakening from clay transformation • Microfracturing associated with reactivated fault zones and shear zones: what it can tell us about deformation history • Episodic weakening and strengthening during synmetamorphic deformation in a deep crustal shear zone in the Alps • Geometric controls and fault system evolution Geometric controls on the evolution of normal fault systems • The nature and origin of asymmetric arrays of shear surfaces in fault zones • A quantitative study of the influence of pre-existing compositional and fabric heterogeneities upon fracture zone development during basement reactivation • Insights from lithosphere- to crustal-scale fault zones Lithospheric and crustal reactivation of an ancient plate boundary: the assembly and disassembly of the Salmon River suture zone, Idaho, USA • Sequential ductile through brittle reactivation of major fault zones along the accretionary margin of Gondwana in Central Argentina • Rheological partitioning during multiple reactivation of the Palaeozoic Brevard Fault Zone, Southern Appalachians, USA • Repeated reactivation in the Apennine-Maghrebide system. Italy: an example of fault zone weakening ? • Weak zones in Precambrian Sweden • The role of fault zones and melts as agents of weakening, hardening and differentiation of the continental crust – a synthesis • Index. Principal Authors: J Townend, Stanford University, USA. A Kopf, Scripps Insitution of Oceanography, USA. I Main, University of Edinburgh, UK. K P Furlong, Pennsylvania State University, USA. L N Warr, Ruprecht-Karls-Universitat, Germany. Y Yan, University of Michigan, USA. G Mitra, University of Rochester, USA. K Steffen, University of New Mexico, USA. J J Walsh, University of Liverpool, UK. S F Wojtal, Oberlin College, USA. L E Beacom, Queen’s University of Belfast, Northern Ireland. B Tikoff, University of Wisconsin, USA. C Simpson, Boston University, USA. R D Hatcher, University of Tennessee, USA. E Tavernelli, Universita di Siena, Italy. C J Talbot, Uppsala University, Sweden. M R Handy, Universite de Lausanne, Switzerland.