Book excerpt: Understanding the functions and properties of molecules in living systems requires a detailed knowledge of their three-dimensional structures and the conformational variability that allows them to adopt multiple functional forms. Interpreting biological systems in the language of three-dimensional structures is of fundamental importance and innumerable research groups around the world are working in this area. This book is a compilation of articles describing attempts at understanding the intricacies of biological systems through the structures of and interactions between their constituent molecules.