This volume comprises papers presented at the 40th Erice Course "From Molecules to Medicine: Structure of Biological Macromolecules and Its Relevance in Combating New Diseases and Bioterrorism", May 29 to June 8, 2008. The papers span the breadth of material presented, which emp- size the practical aspects of modern macromolecular crystallography and its applications to medicine. Topics addressed span from the selection of targets, through to structure determination, interpretation and exploitation. A particular theme that emerges is the dependence of modern structural science on multiple experimental and computational techniques. It is both the development of these techniques and their integration that will take us forward in the future. The NATO ASI directors worked alongside, and offer deep gratitude to Prof. Sir Tom Blundell, Director of the International School of Crystal- graphy, Dr Colin Groom, Dr Neera Borkakoti, Dr John Irwin and Prof. Lodovico Riva di Sanseverino, who were in turn supported by a number of local facilitators. The course was financed by NATO as an Advanced Study Institute. Additional support was given by the European Crystallographic Association, the International Union of Biochemistry and Molecular Biology, the Int- national Union of Crystallography, the University of Bologna, AstraZeneca, Roche, Merck & Co., Boehringer Ingelheim, Bruker Corporation, Douglas Instruments, Informa UK, the Department of Pharmaceutical Chemistry, TTP Lab Tech, University of California at San Francisco. Joel L. Sussman and Paola Spadon