Interplanetary contamination refers to biological contamination of a planetary body by a space probe or spacecraft, either deliberate or unintentional.

There are two types of interplanetary contamination:

The main focus is on microbial life and on potentially invasive species. Non biological forms of contamination have also been considered including e.g. contamination of sensitive deposits (such as lunar polar ice deposits) of scientific interest by rocket exhausts. In the case of back contamination, multicellular life is thought unlikely but not been ruled out, and in case of forward contamination, then again, forward contamination by multicellular life (e.g. lichens) becomes a consideration in human missions, though unlikely for robotic missions.