This book offers an in-depth exploration of the synthesis, design, and applications of two-dimensional semiconductors for clean energy solutions and technologies. These semiconductor nanostructures serve as a transformative platform, with tunable properties arising from quantum confinement and unique surface phenomena, making them essential for innovation in electronics, photonics, energy storage, energy conversion, and sensing. This book examines the cutting-edge roles of nanosheets, nanowires, and other two-dimensional semiconductor nanostructures, highlighting their capabilities in next-generation electronics, optoelectronics, and energy applications. Through detailed case studies and analysis, it explores how size-dependent properties, such as tunable luminescence and surface phenomena, make these materials suitable for miniaturized, high-performance devices and innovative energy solutions, including advanced photovoltaics, batteries, and fuel cells. It also highlights recent advancements in semiconductor-based devices for applications such as photovoltaics, wastewater treatment, and fuel cells. Addressing both key progress and ongoing challenges, this resource offers researchers a foundation for exploring the potential of two-dimensional nanomaterials. Detailed discussions on controlling parameters make it a valuable guide for early-career researchers seeking to understand and leverage these materials.