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Endospores are non-reproductive forms produced by certain Gram-positive rods, especially Bacillus and Clostridium. Nutrient depletion can trigger sporulation, during which asymmetric division and protective layers help form a mature spore. Its dehydrated, metabolically inactive core contains dipicolinic acid–calcium and DNA-binding proteins, while the cortex, coat, and sometimes exosporium add protection. These features help spores resist heat, drying, radiation, chemicals, and other stresses. Spores can return to vegetative growth when germination is triggered by nutrients and water uptake. Their persistence is relevant to environmental and food contamination, laboratory identification, and sterilization validation. Understanding these connections helps explain both the clinical importance of spore-forming bacteria and the need for effective methods to destroy spores.