Earth's atmosphere offers little protection against comet impacts, because many comets are bigger than 1 km. Fewer comets hit Earth than asteroids of the same size, except perhaps for sizes larger than 10 km. Comets release copious amounts of solid debris called meteoroids, and these meteoroids disperse to form meteoroid streams, some of which cause meteor showers on Earth. Recent meteor shower observations reveal the presence of potentially dangerous parent comets and trace their dynamical evolution. In addition, some showers leave a signature of “cosmic dust” in our atmosphere.