Twelfth edition, 2009 of this book is based on IS: 800-2007 and also newly revised IS: 883-1994 (code of practice for timber structures). New code of practice, IS: 800 is likely to be issued soon. It is likely to introduce ``Limit State Design of Steel Structures''. Authors have distributed the text in thirty four chapters in main text and one chapter `on Location of Shear Centre' in Appendix A. Concept of Shear Centre and bending axis is important and significant and essentially needed to understand simple theory of bending and so also unsymmetrical bending. Complete-text has been updated and new matter added (e.g., elastic buckling, inelastic, stability and instability of columns and compression members, torsional-buckling, torsional-flexural buckling, etc.). Behaviour of web-stiffeners and web-panels specially near the end panels, tension-field action has been first time included to familiarise the students with the concept. Durability of steel members have been emphasized phenomenon of corrosion has been distinctly explained.