Catheters are flexible tubes used in medicine to introduce fluids into or withdraw fluids from the body, or to keep a passage open. They are versatile medical devices employed in various specialties. Common types include urinary catheters, which drain urine from the bladder (e.g., Foley catheters for indwelling use, intermittent catheters for temporary drainage); intravenous (IV) catheters, inserted into veins for administering fluids, medications, or drawing blood; and cardiac catheters, used in diagnostic and interventional cardiology procedures to access the heart and blood vessels. Catheters come in various materials (e.g., silicone, latex, PVC) and sizes, tailored for specific medical purposes. Their application requires sterile technique to prevent infection. Catheters are fundamental tools for monitoring, diagnosis, and treatment across a broad spectrum of medical conditions, from simple hydration to complex surgical interventions.