This book concerns the broad domain of reconfigurable architectures and more specifically FPGAs. Different issues that are the centre of this book are very essential and are intended to overcome the current limitations of FPGAs, which are experiencing extremely rapid and sustained development for several years. In fact, FPGAs offer a particularly remarkable flexibility but suffer from a level of performance that can be disadvantageous for some applications in terms of surface, speed or energy. This work presents several significant and original contributions in order to remove these limitations by focusing especially on the surface metric. This book aims at exploring heterogeneous FPGA architectures dedicated to a given set of application circuits. Beyond architecture exploration, this work also presents automatic FPGA "layout" generation flow, and a new component called as an ASIF "Application Specific Inflexible FPGA", which significantly reduces silicon footprint by customizing the architecture for a given set of applications circuits. The importance and originality of the contributions made in this work revolve around this new concept of application specific reconfigurable circuits, mainly the development of an entire design environment including: generation tools, floor-planning, placement and routing adapted to the case of heterogeneous blocks. Careful analysis of results and the validation of proposed techniques have also been observed. The monograph of this book is based on Husain’s doctoral thesis. It was a great pleasure for me to supervise his thesis. This book will be of special interest for students and researches in the domain of FPGA architectures in general, and application-specific FPGA architectures, heterogeneous FPGA architectures, and their automatic hardware generation in particular.