Polycapillary optics is a specialized field within X-ray optics concerned with the design, fabrication, and application of structured glass devices containing numerous microscopic capillaries. This concept investigates the principles and characteristics of guiding divergent X-ray beams through these capillaries via total external reflection, focusing on efficiently collecting, collimating, or focusing the radiation. Its significance lies in enhancing signal intensity, improving coupling efficiency to detectors or analyzers, and enabling high-resolution analysis in various X-ray spectroscopic and imaging techniques.