It’s a question that we have pondered for years: is life on earth really the only life that’s out there in the universe? Turns out there’s a good chance it’s not just us. With research indicating that other planets might be able to host life, how should we be thinking about interactions between extraterrestrial and Earth life? Planetary protection involves avoiding contamination of other locations in the universe with Earth life, as well as preventing unpleasant things happening when possibly-inhabited material is brought to Earth from other planets. How can we tell the difference between extraterrestrial and Earth life? What do we need to keep Earth safe, and other planets safe from contamination by us?