Book excerpt: This Research Topic is the second volume of the 'Community series-Extremophiles: Microbial Genomics and Taxogenomics'. Please see the first volume here. Extreme habitats exist across the globe and span over three quarters of our planet. They can be widely different from a physical-chemical perspective as they include diverse types of extreme, such as temperature, pH, salinity, radiation, pressure, low water activity, low nutrient availability, etc. Organisms capable of adjusting, surviving, or thriving in those habitats, which are so hostile that they were previously thought to be adverse or lethal for life, are called “extremophiles”.