In 1989, the American Institute of Steel Construction published the ninth edition of the Manual of Steel Construction which contains the "Specification for Structural Steel Buildings-Allowable Stress Design (ASD) and Plastic De­ sign." This current specification is completely revised in format and partly in content compared to the last one, which was published in 1978. In addition to the new specification, the ninth edition of the Manual contains completely new and revised design aids. The second edition of this book is geared to the efficient use of the afore­ mentioned manual. To that effect, all of the formulas, tables, and explanatory material are specifically referenced to the appropriate parts of the AISCM. Ta­ bles and figures from the Manual, as well as some material from the Standard Specifications for Highway Bridges, published by the American Association of State Highway and Transportation Officials (AASHTO), and from the Design of Welded Structures, published by the James F. Lincoln Arc Welding Foun­ dation, have been reproduced here with the permission of these organizations for the convenience of the reader. The revisions which led to the second edition of this book were performed by the first two authors, who are both experienced educators and practitioners.