Free fatty acids (FFAs) have antibacterial properties that allow them to kill or inhibit the growth of bacteria. Many organisms use FFAs to defend against parasitic or pathogenic bacteria. The primary target of FFA action is the cell membrane, where FFAs disrupt the electron transport chain and oxidative phosphorylation. FFAs can also inhibit enzyme activity, impair nutrient uptake, generate peroxidation and auto-oxidation products, or directly lyse bacterial cells. Their broad spectrum of activity, non-specific mode of action, and safety make them attractive as antibacterial agents in medicine, agriculture, and food preservation, especially where conventional antibiotics are not desirable or prohibited. The evolution of inducible FFA-resistant phenotypes is less problematic than with conventional antibiotics. The potential for commercial or biomedical use of antibacterial FFAs, especially those from natural sources, is discussed. Fatty acids (FAs) are common molecules found in lipids, which are essential components of cell structures such as membranes and energy stores. FAs can be released from lipids by enzyme action to become FFAs, which have diverse biological activities. FFAs consist of carbon chains with a carboxyl group at one end and a methyl group at the other. They are amphipathic, with a hydrophilic carboxyl group and a hydrophobic carbon chain. Short-chain FFAs have fewer than 8 carbon atoms, while long-chain FFAs have more than 16. Unsaturated FFAs have double bonds in their carbon chains, while saturated FFAs have only single bonds. Lipases, which break down lipids to release FFAs, can be specific to certain lipids or FAs based on their position and structure. FFAs play a role in host defense against pathogens by inhibiting bacterial growth or directly killing bacteria.Free fatty acids (FFAs) have antibacterial properties that allow them to kill or inhibit the growth of bacteria. Many organisms use FFAs to defend against parasitic or pathogenic bacteria. The primary target of FFA action is the cell membrane, where FFAs disrupt the electron transport chain and oxidative phosphorylation. FFAs can also inhibit enzyme activity, impair nutrient uptake, generate peroxidation and auto-oxidation products, or directly lyse bacterial cells. Their broad spectrum of activity, non-specific mode of action, and safety make them attractive as antibacterial agents in medicine, agriculture, and food preservation, especially where conventional antibiotics are not desirable or prohibited. The evolution of inducible FFA-resistant phenotypes is less problematic than with conventional antibiotics. The potential for commercial or biomedical use of antibacterial FFAs, especially those from natural sources, is discussed. Fatty acids (FAs) are common molecules found in lipids, which are essential components of cell structures such as membranes and energy stores. FAs can be released from lipids by enzyme action to become FFAs, which have diverse biological activities. FFAs consist of carbon chains with a carboxyl group at one end and a methyl group at the other. They are amphipathic, with a hydrophilic carboxyl group and a hydrophobic carbon chain. Short-chain FFAs have fewer than 8 carbon atoms, while long-chain FFAs have more than 16. Unsaturated FFAs have double bonds in their carbon chains, while saturated FFAs have only single bonds. Lipases, which break down lipids to release FFAs, can be specific to certain lipids or FAs based on their position and structure. FFAs play a role in host defense against pathogens by inhibiting bacterial growth or directly killing bacteria.