This book presents a novel approach for Architecture Description Language (ADL)-based instruction-set description that enables the automatic retargeting of the complete software toolkit from a single ADL processor model. This allows a high speedup in compiler generation and contributes to a more efficient ASIP design flow. Coverage includes a comprehensive overview of retargetable compilers and ADL based processor design, a methodology and related toolkit to generate a C-compiler fully automatically from an ADL processor model, and retargetable code optimization techniques to achieve retargetability and high code quality for two common architecture classes.