3200 Phaethon (sometimes incorrectly spelled Phaeton) is an Apollo and Mercury-, Venus- and Mars_crosser asteroid with unusual properties, and may be an extinct comet.

Simon Green and John K. Davies, while searching Infrared Astronomical Satellite (IRAS) data for moving objects, discovered 3200 Phaethon (1983 TB) in images from October 11, 1983. It was announced on October 14 in IAUC 3878 along with optical confirmation by Charles T. Kowal, who reported it to be asteroidal in appearance. IAUC 3881 soon reported Fred Whipple's observation that "orbital elements of 1983 TB shown on IAUC 3879 are virtually coincident with the mean orbital elements of 19 Geminid meteors photographed with the super-Schmidt meteor cameras". Phaethon thus turned out to be the long-sought parent body of the Geminids meteor shower.

Phaethon's most remarkable distinction is that it approaches the Sun closer than any other numbered asteroid; its perihelion is only 0.140 AU —, which is 58% of Mercury's orbital radius). The surface temperature at perihelion could reach ~1025 K. For this reason, it was named after the Greek myth of Phaëton, son of the sun god Helios.

Phaethon's attributes (orbit, size, reflectivity, and association with an annual meteor shower) can be argued as being cometary, except that Phaethon has never been caught exhibiting a coma, gas jets, or dust trail. Thus it is classified as an Apollo asteroid but is believed to be an inactive or extinct comet nucleus.

Phaethon is classified as a B-type asteroid because it is composed of dark material; this too fits well with the cometary origin hypothesis. It measures 5.10 km in diameter.

Phaethon will approach relatively close to the Earth on December 14, 2093, passing within 0.0194 AU (2.9 Gm).