The catastrophic earthquakes of the last decades (Mexico City, 1985, Loma Prieta, 1989, Northridge, 1994, Kobe, 1995) have seriously undermined there putation of steel structures, which in the past represented the most suitable solution for seismic resistant structures. Even if in very few cases, the performance of steel joints and members was unexpectedly bad, showing that it was due to some lacks in the current design concept. As a consequence of the lessons learned from the above dramatic events, many progress has been recently achieved in the conception, design and construction, by introducing the new deals of the performance based design, including the differentiation of earthquaketypes and considering all factor influencing the steel structure behaviour under strong ground motions. In this scenario, the aim of the book is to transfer the most recent achievements into practical rules for a safe design of seismic resistant steel structures. The seven Chapters cover the basic principles and design criteria for seismic resistant steel structures, which are applied to the main structural typologies, like moment resistant frames, braced frames and composite structures with particular reference to connections and details.