Bacteria import and/or synthesize the amino acids required for their metabolism and physiological functions. Not all bacteria synthesize all the required amino acids, therefore numerous bacteria depend on extracellular supply. The carbon backbones of amino acids can originate from different precursors including 11 amino acids, and among these amino acids, 3 of them can give rise to 9 other amino acids. Amino acids can be synthesized by diverse metabolic pathways in the different bacterial species studied, indicating metabolic variations in bacteria for amino acid synthesis. The synthesis of several amino acids requires energy in the form of ATP, and ammonia and hydrogen sulfide are notably used as precursors in several metabolic steps. Although numerous metabolic pathways for amino acid biosynthesis are common to bacteria and archaea, several metabolic pathways are much different when comparing these living cells, and several metabolic pathways found in archaea are not found in bacteria. Bacteria and archaea use however similar strategy for the incorporation of amino acids in RNAs and DNA. Bacteria use a subset of amino acids for ATP production and amino acid-derived bacterial metabolites participate in processes implicated in bacterial growth, virulence, toxin production, biofilm formation, respiration, resistance to acidity and osmotic stress, as well as resistance to antibiotics, thus establishing their roles in main processes linked to bacterial metabolism and physiology.