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LPS is found in Gram-negative bacteria and is absent from Gram-positive bacteria. It has three parts: Lipid A, the toxic moiety; a core polysaccharide; and a variable O-antigen side chain used in serotyping and associated with immune evasion. Lipid A activates TLR-4/CD14 on immune cells, promoting inflammatory mediator release. Excessive responses can contribute to fever, hypotension, capillary leak, septic shock, disseminated intravascular coagulation, and multiorgan failure. LPS is heat-stable and is released mainly through bacterial lysis or membrane blebs rather than active secretion. It also affects complement and coagulation pathways. These structural and functional features help explain its role in bacterial identification, host responses, and clinical complications.