Bacillus endospores are highly resistant to extreme terrestrial and extraterrestrial environments. This review discusses the molecular mechanisms underlying spore resistance, focusing on Bacillus subtilis 168 and its relatives. Spores are dormant, metabolically inactive structures that can survive for millions of years in various environments. Spore resistance is influenced by factors such as genetic makeup, sporulation conditions, spore coat structure, core permeability, core water content, core mineral content, and the presence of α/β-type SASP (small acid-soluble proteins). These factors contribute to spore resistance to heat, UV radiation, gamma radiation, desiccation, and other environmental stresses. Spores resist heat by having a low core water content and high mineral content, which stabilizes proteins and DNA. Spore DNA is protected by α/β-type SASP, which binds to DNA and prevents damage. Spores also have repair mechanisms that allow them to fix DNA damage during germination. Spore resistance to UV radiation is enhanced by the formation of the spore photoproduct (SP), which is efficiently repaired by spore-specific DNA repair systems. Spores are also resistant to γ-radiation, though the exact mechanisms are not fully understood. Spores can survive extreme pressures, including those found in deep-sea environments and space. Spore resistance to high hydrostatic pressure is due to their ability to germinate and then be killed by pressure. Spores germinated at higher pressures remain resistant to UV and oxidizing agents, likely due to the protection provided by α/β-type SASP. Spore DNA repair mechanisms include nucleotide excision repair (NER), recombination-mediated repair, and other general repair systems. Spores also have a specific DNA repair system, SP Lyase, which repairs SP. Spore resistance to environmental stresses is influenced by the ability to repair DNA damage during germination. Spores can be transported through space and may contribute to the transfer of life between planets. Understanding spore resistance mechanisms is important for assessing the potential for microbial life to survive in extreme environments.Bacillus endospores are highly resistant to extreme terrestrial and extraterrestrial environments. This review discusses the molecular mechanisms underlying spore resistance, focusing on Bacillus subtilis 168 and its relatives. Spores are dormant, metabolically inactive structures that can survive for millions of years in various environments. Spore resistance is influenced by factors such as genetic makeup, sporulation conditions, spore coat structure, core permeability, core water content, core mineral content, and the presence of α/β-type SASP (small acid-soluble proteins). These factors contribute to spore resistance to heat, UV radiation, gamma radiation, desiccation, and other environmental stresses. Spores resist heat by having a low core water content and high mineral content, which stabilizes proteins and DNA. Spore DNA is protected by α/β-type SASP, which binds to DNA and prevents damage. Spores also have repair mechanisms that allow them to fix DNA damage during germination. Spore resistance to UV radiation is enhanced by the formation of the spore photoproduct (SP), which is efficiently repaired by spore-specific DNA repair systems. Spores are also resistant to γ-radiation, though the exact mechanisms are not fully understood. Spores can survive extreme pressures, including those found in deep-sea environments and space. Spore resistance to high hydrostatic pressure is due to their ability to germinate and then be killed by pressure. Spores germinated at higher pressures remain resistant to UV and oxidizing agents, likely due to the protection provided by α/β-type SASP. Spore DNA repair mechanisms include nucleotide excision repair (NER), recombination-mediated repair, and other general repair systems. Spores also have a specific DNA repair system, SP Lyase, which repairs SP. Spore resistance to environmental stresses is influenced by the ability to repair DNA damage during germination. Spores can be transported through space and may contribute to the transfer of life between planets. Understanding spore resistance mechanisms is important for assessing the potential for microbial life to survive in extreme environments.