This book serves as a background for students in Structural and Civil Engineering. Since the available hours for teaching Steel Structures and particularly Tubular Structures vary from country to country, this book has been written in a modular form. To cover the needs in the various countries, a committee was established to review the material. Although the material is mainly based on the Eurocodes, the setup makes it easy to change the lectures and relate them to other (national) codes. Design is an interactive process between the functional and architectural requirements and the strength and fabrication aspects. In a good design, all these aspects have to be considered in a balanced way. Due to the special features of hollow sections and their connections it is even here of more importance than for steel structures of open sections. The designer should therefore be aware of the various aspects of hollow sections, as basically described in this book.