npj Extreme Ecosystems considers research exploring all aspects of extreme environments and their ecological extensions on understanding how organisms survive, adapt, and evolve under extreme physical and chemical conditions. This journal aims to explore the interplay between extreme environments, climate change, and extremophiles across terrestrial, aquatic, and deep subsurface realms as well as to unveil Earth-analogs for extraterrestrial environments. The journal covers a board range of topics including but not limited to: - Characteristics of extreme environments - Geophysical, biogeochemical, and bioenergetic processes of extreme environments - Biotic and abiotic interactions in extreme environments - Ecosystem structure, function, services in extreme environments - Extremophiles and their habitability in extreme environments - Responses, adaptation, and evolution of extremophiles to climate change - Earth-analogs for extraterrestrial environments.