R.I.G Hughes offers an original approach to the philosophical understanding of physics: instead of examining theories, he examines the theoretical practices which physicists use. He starts with a critical study of the accounts that physicists give of their practices, and asks: Given that these practices are successful, what is the nature of their success? Eight of the nine essays are illustrated by case studies of particular episodes in the history of physics. In three essays these case studies are strictly historical; the others deal with physics since 1900. Three essays deal with standard topics in the philosophical literature (laws, explanation, and realism), but are here considered from the perspective that an examination of theoretical practice affords. The five essays at the centre of the book all deal with different aspects of modelling in physics. Another examines the discourse of physics, in particular the languages in which physical narratives are told and experimental work is described. The final essay draws out the implications of the earlier essays for the thesis of scientific realism.