This book presents reviews of various aspects of radiation/matter interactions, be these instrumental developments, the application of the study of the interaction of X-rays and materials to a particular scientific field, or specific methodological approaches. The overall aim of the book is to provide reference summaries for a range of specific subject areas within a pedagogical framework. Each chapter is written by an author who is well known within their field and who has delivered an invited lecture on their subject area as part of the “RX2009 – X-rays and Materials” colloquium that took place in December 2009 at Orsay in France. The book consists of five chapters on the subject of X-ray diffraction, scattering and absorption. Chapter 1 gives a detailed presentation of the capabilities and potential of beam lines dedicated to condensed matter studies at the SOLEIL synchrotron radiation source. Chapter 2 focuses on the study of nanoparticles using small-angle X-ray scattering. Chapter 3 discusses the quantitative studies of this scattering signal used to analyze these characteristics in detail. Chapter 4 discusses relaxor materials, which are ceramics with a particularly complex microstructure. Chapter 5 discusses an approach enabling the in situ analysis of these phase transitions and their associated microstructural changes.