<p>Chirality is a fundamental geometric property that manifests across molecular and nanoscale systems, profoundly influencing physical, chemical, and biological processes. At the intersection of chiral chemistry and nanoscience, chiral nanomaterials have emerged as a transformative class of materials, exhibiting unique spin-dependent properties governed by the chiral-induced spin selectivity (CISS) effect. This quantum phenomenon, rooted in spin-orbit coupling and spin filtering mechanisms, enables precise modulation of electron spin polarization, unlocking new opportunities in catalysis, spintronics, and energy conversion. This review provides a comprehensive overview of the CISS effect in chiral nanomaterials, elucidating its underlying mechanisms—including spin-orbit interactions, spin filtering, and spin blockade—and surveying advanced techniques for characterizing both structural chirality and spin polarization. We further highlight emerging applications in electrocatalysis, photocatalysis, and spintronic device engineering. Despite significant progress, key challenges remain in unraveling the fundamental physics, achieving accurate spin characterization, and translating these phenomena into robust, scalable technologies. Continued interdisciplinary research into the rational design and functionalization of chiral nanomaterials is poised to drive breakthroughs in sustainable energy, next-generation catalysis, and quantum information technologies.</p>