This publication describes and discusses the aspects and issues in EN 1998-1:2004 that need clarification and/or further development. This book is the result of the activities carried out within the framework of technical Committee "Seismic Design" (TC13) of the European Convention for Constructional Steelwork (ECCS) in the field of codification and technical specifications. The publication is organized in twelve Sections and one Annex. The basic topics discussed in the text are "material overstrength", "selection of steel toughness", "local ductility", "design rules for connections in dissipative zones", "new links in eccentrically braced frames", "behaviour factors", "capacity-design rules", "design of concentrically braced frames", "dual structures", "drift limitations and second-order effects", "new structural types" and "low-dissipative structures".