This comprehensive textbook focuses on the torsion in thin walled structures, highlights the nuances of the problems faced and succinctly discusses warping, bimoment, etc. Since in several thin walled structures, torsion is the only or dominant loading, this book addresses such unique structures as well. It provides a concise explanation of the warping properties and how they are evaluated. Thin walled structures with torsion as the preponderant loading are then treated using classical and finite element methods. No prior knowledge of the finite element method is required as the method is introduced from the basics. The same problem is worked out by both approaches so that the concepts are clearly understood by the readers. The book includes pedagogical features such as end-of-chapter questions and worked out examples to augment learning and self-testing. The book will be useful for graduate courses as well as for professional development coursework for structural engineers in the aerospace, mechanical, and civil engineering domains.