In medicine, a catheter (/ˈkæθətər/[1] KA-thə-tər) is a thin tube made from medical grade materials serving a broad range of functions.

Functionally, they allow drainage, administration of fluids or gases, access by surgical instruments, and also perform a wide variety of other tasks depending on the type of catheter.

[2] Special types of catheters, also called probes, are used in preclinical or clinical research for sampling of lipophilic and hydrophilic compounds,[3] protein-bound and unbound drugs,[4][5] neurotransmitters, peptides and proteins, antibodies,[6][7][8] nanoparticles and nanocarriers, enzymes and vesicles.

[9] Placement of a catheter into a particular part of the body may allow: Ancient Chinese used onion stalks, the Romans, Hindus, and Greeks used tubes of wood or precious metals.

Franklin's catheter was made of metal with segments hinged together with a wire enclosed to provide rigidity during insertion.

[16] In 1929, Werner Forssman first performed central venous catheterization,[17] work which led to the development of cardiac catherization as a treatment, for which he, André F. Cournand and Dickinson W. Richards would win the Nobel Prize for Medicine in 1959.

[18] Central venous catheterization allows for continuous administration of medications, fluids and blood products to a large vein, particularly in critically ill patients.

[23] A range of polymers are used for the construction of catheters, including silicone rubber, nylon, polyurethane, polyethylene terephthalate (PET), latex, and thermoplastic elastomers.

[24][25][26] For example, silicone is used in Foley catheters where fractures have been reported, often requiring surgery to remove the tip left in the bladder.

Depending on the mechanical characteristics required, assorted polymers and polymer-metal composites can be used to build catheters used for interventional purposes.

Common materials include polyamide (nylon), polyether block amide, polyuerathane, polyethylene terephthalate, and polyimides.

Radiocontrast agent is then injected through the catheter to visualise the vessels via various imaging methods such as computed tomography (CT), projectional radiography, and fluoroscopy.