Polonium (Po) is a radioactive chemical element with atomic number 84. It is a hazardous substance to humans and is very dangerous, often lethal, to inhale or ingest.

Polonium is a very rare element, it comes only from the decay of heavier radioactive elements like uranium and radium. Polonium is only found in nature (in trace amounts) as the isotope ²¹⁰Po, with a half-life of 138 days.