This chapter synthesizes how nanoscale phenomena—quantum tunneling and confinement, large surface-to-volume ratios, ballistic transport, anisotropic carrier motion in low-symmetry 2D materials, and plasmonics—reshape device physics and enable new electronic–photonic functionalities. It surveys key nanomaterials—graphene/CNTs, quantum dots, TMDs, and metal-oxide nanostructures—and their roles in flexible/wearable platforms, nanosensors, energy systems, and optoelectronics. The chapter then reviews fabrication toolkits spanning top-down lithographies and bottom-up growth (CVD/ALD) that underpin modern nano-integration, followed by device-level advances from FinFETs to gate-all-around FETs that extend electrostatic control past planar scaling. It highlights nanotechnology’s contributions to quantum computing—materials, structures, and coherence considerations for scalable qubits—before assessing energy-efficient nanoelectronics, including low-power memories and architectures, alongside energy harvesting and storage themes. Finally, it connects these threads to optoelectronic devices (e.g., high-bandwidth graphene/TMD photodetectors) and concludes with challenges in stability, manufacturability, and reliable control at atomic dimensions that will steer the next wave of nanoelectronic technologies.