<p>High-performance electron-transporting semiconducting polymers are indispensable for the realization of flexible and fully plastic electronic devices. Their molecular design fundamentally relies on the incorporation of strongly electron-deficient building units that stabilize reduced states and promote efficient electron-transport processes. The creation of new electron-deficient units therefore remains a central challenge in the research field of semiconducting polymers. This Focus Review summarizes our recent efforts toward the rational design of electron-transporting semiconducting polymers on the basis of strongly electron-deficient building motifs, which are categorized into imide-functionalized heteroaromatics, naphthobisthiadiazole and related heteroaromatics, and fused and nonfused thienoquinoid systems. Polymers incorporating these building units exhibited low-lying lowest-unoccupied-molecular-orbital (LUMO) energy levels and efficient solid-state organization schemes, resulting in enhanced electron mobility. Across these systems, several unique molecular design strategies have emerged to ensure electron-transport pathways, involving the enforcement of backbone planarity through noncovalent intramolecular interactions, the promotion of intermolecular charge transport via multiple noncovalent contacts, and the enhancement of the intrachain charge transport process through extended π-electron delocalization. This review provides important guidelines for new rational molecular designs of high-performance electron-transporting semiconducting polymers.</p>