This book reports on the design, fabrication and characterization of a set of flexible electronic components, including on-foil sensors, organic thin-film transistors and ultra-thin chips. The core of the work is on showing how to combine high-performance integrated circuits with large-area electronic components on a single polymeric foil, to realize smart electronic systems for different applications, such as temperature, humidity and mechanical stress sensors. The book offers an extensive introduction to Hybrid System-in-Foil technology (HySiF), and related on-chip/on-foil passive and active components. It presents six case studies designed to highlight key HySiF challenges, together with the methodology to address those challenges. Last but not least, it describes the development of a reconfigurable, energy-efficient Analog-to-Digital Converter for HySiF. All in all, this book provides readers with extensive information on the state of the art in the design and characterization of integrated circuits and hybrid electronic systems on flexible polymeric substrates. By describing significant advances in organic thin-film transistor technology, this work is expected to pave the way to future developments in the area of energy-efficient smart sensors and integrated circuits.