Book excerpt: Migmatites are highly heterogeneous rocks found in high-grade metamorphic environments; they are commonly encountered in the continental crust. Until now, many geologists have been deterred from working with migmatites because of their complex appearance and an unhelpful non-genetic nomenclature. In his Atlas of Migmatites, Dr. Edward Sawyer provides genetically based definitions and a system of nomenclature with which it will be possible to describe and map migmatites effectively and to understand how combinations of factors and processes produce a bewildering morphological diversity. Migmatites are produced by partial melting; to aid the reader in the identification of migmatites, the author describes and illustrates microstructures that can be used to infer the presence of melt or a melt-producing reaction. He also describes how geochemical data can be used to infer petrological processes involved in migmatite development. This book includes the results from two decades of research in whole-rock geochemistry, partial melting, microstructural analysis and experimental deformation of partially molten rocks. It contains information from an outcrop through to a grain scale. Exceptionally well illustrated, with 272 colour plates and accompanying detailed captions, the Atlas provides descriptions and analyses of migmatites not previously available.