The Period Circadian Regulator 3 (PER3) protein is a key component of the circadian clock machinery, which regulates daily physiological and behavioral rhythms in mammals. Encoded by the *PER3* gene, it interacts with other core clock proteins (e.g., PER1/2. CRY1/2) to form negative feedback loops that drive 24-hour oscillations in gene expression. PER3 is particularly noted for its role in modulating sleep-wake cycles, metabolic processes, and responses to environmental light. Antibodies targeting PER3 are essential tools for studying its expression, localization, and function in circadian biology. These antibodies are widely used in techniques like Western blotting, immunohistochemistry, and immunofluorescence to detect PER3 in tissues such as the brain, liver, and peripheral blood cells. Research using PER3 antibodies has linked its dysregulation to sleep disorders (e.g., delayed sleep phase syndrome), mood disorders, and metabolic syndromes. Additionally, studies suggest PER3 polymorphisms may influence individual susceptibility to shift-work-related health issues or cancer progression. Commercial PER3 antibodies are typically raised against specific epitopes (e.g., human PER3 N- or C-terminal regions) and validated for cross-reactivity in model organisms like mice. Their application continues to advance understanding of circadian disruptions in disease contexts, making them critical for both basic and translational chronobiology research.