Code clones are recurring similar program structures. Several techniques exist to detect similar code fragments (simple clones) for better software maintenance, but further gains can be obtained by by detecting similar classes, source files or directories. Structural clones embody such large-granularity, design-level similar program structures that often map to design or application domain concepts. Detection of structural clones leads to a better understanding of the design of the system, easing software maintenance, evolution, and re-engineering. Unification of structural clones with generic program structures helps in program simplification and reuse. This book introduces structural clones and describes a technique for their systematic detection. The usefulness and scalability of the proposed method is validated via experimentation using the structural clone detection tool 'Clone Miner'. Structural clones also offer opportunities for unconventional reuse that reaches beyond reuse rates achievable with architecture- centric, component-based approaches, and also brings reduction of cognitive program complexity.