Organic and hybrid organic-inorganic semiconductors have been envisioned for several optoelectronic and energy applications where mechanical flexibility, light weight, and low-temperature fabrication processes possibly by printing are major advantage over silicon. This presentation will describe the design rationale, synthesis, and characterization of representative semiconducting materials for flexible thin-film transistors (TFTs), displays, and organic solar cells. Our research aims at understanding how their properties/charge-transport characteristics are affected by molecular design/composition, synthetic methodology, thin-film processing parameters, film morphology/microstructure, and device architecture. Particularly, we will focus on naphthalenediimide (NDI) and isomeric benzothiadiazole (isoBT) polymers starting from their synthetic access, approaches to backbone planarization and tuned p-conjugation and how these chemical modifications affect, among other properties, film and device mechanical flexibility and stretchability. Furthermore, new semiconducting metaloxide-polymer alloys are discussed as representative of flexible hybrid semiconductors enabling, among other properties, optical transparency in the visible.