This book presents a comprehensive introduction to an advanced beam theory applicable to thin-walled beams of rectangular and arbitrarily-shaped cross-sections. Furthermore, it describes a unique beam-based approach to handling joint structures consisting of thin-walled beams, compiled here for the first time. This higher-order beam theory (HoBT), developed by the authors over the past two decades, uses more than six degrees of freedom (DOFs) in contrast to the classical theories, which use only six DOFs. The additional degrees of freedom describe sectional deformations such as warping and distortion. This book presents a novel systematic procedure to derive the sectional deformations analytically for rectangular cross-sections and numerically for arbitrarily-shaped cross-sections. This book is a must for structural mechanical engineers who wish to understand design structures involving thin-walled beams.