Bile acids play a fundamental role in the degradation and absorption of intestinal lipids. The primary ones are cholic acid and chenodeoxycholic acid which are synthesized from cholesterol in the liver and conjugate with taurine and glycine amino acids. The secondary bile acids are derived from the primary ones by the enzyme action of intestinal bacteria through a process of deconjugation and dehydroxylation. Their detergent property is based on the molecular configuration of these compounds, which present a hydrophilic and a hydrotion of these compounds, which present a hydrophilic and a hydrophobic surface. The different enzymes in the liver cells that intervene in the process of synthesis of bile acids are now known. A basic element in their physiology is the enterohepatic circulation, enabling the organism to take maximum advantage of these compounds. The dynamics of the cycle are maintained and regulated by the system of uptake and secretion of the cells, cholecystokinin, intestinal peristalsis, active transport across the ileal membrane, and by portal venous flow. Much of our knowledge about the biogenesis and functions of the bile acids has been acquired quite recently. Research over the past three decades has contributed to a great advance in our understanding of their physiology.