Unified Design of Steel Structures, 3rd edition, continues the unified LRFD and ASD approach to teaching structural steel design established in the first two editions. It addresses the design of steel structures for buildings as governed by the ANSI/AISC 360-16 Specification for Structural Steel Buildings, published by the American Institute of Steel Construction (AISC). It is intended primarily as a text for a first course in steel design for civil and architectural engineers. Such a course usually occurs in the third or fourth year of an engineering program. The book can also be used in a second, building-oriented course in steel design, depending on the coverage in the first course. In addition to its use as a textbook, it provides a good review for practicing engineers looking to learn the provisions of the latest specification or to convert their practice from any of the old specifications to the new specification. Users are expected to have a firm knowledge of statics and strength of materials and have easy access to the AISC Steel Construction Manual, 15th Edition. All examples that rely on LRFD and ASD provisions are fully presented, even if it means some duplication, so that regardless of approach being taught, there will be no need to refer to the other approach example. All homework problems that could be LRFD or ASD are presented both ways so that the instructor may choose the approach they want the student to follow. Subjects addressed include: principles of limit states design; load factors, resistance factors, and safety factors; tension member design; column or compression member design; beam or bending member design; plate girder design; design of beam-columns or members subjected to combined axial load and bending; bracing member design; composite member design; connection basics including bolts, welds, and connecting elements; design of shear connections, light bracing connections and direct bearing connections; design of moment connections; and basics of seismic design. Unified Design of Steel Structures, 3rd edition, also features multi-chapter problems and a new Integrated Design Project. Instructors can add a few, selected problems throughout the term, or include a full project, design of a four-story office building. Either way, all of the tools are here to help students learn how to apply the AISC Specification to the design of a structural steel building. Sample pages from the AISC Steel Construction Manual can be found throughout the book. Students can easily reference design aids and quickly learn how to use them. Keywords: steel design, beam design, column design, beam-column design, composite design, connection design, AISC