Tempel 1 is a periodic comet (formally designated 9P/Tempel 1). It was discovered on April 3, 1867 by Ernst Wilhelm Leberecht Tempel, an astronomer working in Marseille. At the time of discovery, it approached perihelion once every 5.68 years until 1881. However, every so often, Tempel 1 passes close to Jupiter, which distorts its orbit and changes its orbital period. Its current period is 5.5 years.

Tempel 1 is not a bright comet; its maximum magnitude so far has been 11, far below naked eye visibility. Its diameter is believed to be 6 km.

In July 2005, Tempel 1 will be impacted by the NASA Deep Impact probe, which will gouge a 100 metre crater into its surface. The purpose is to study the interior composition of a cometary nucleus.