L-Carnitine is an endogenous molecule involved in fatty acid metabolism, biosynthesized within the human body using amino acids: L-lysine and L-methionine, as substrates. L-Carnitine can also be found in many foods, but red meats, such as beef and lamb, are the best choices for adding carnitine into the diet. Good carnitine sources also include fish, poultry and milk. Essentially, L-carnitine transports the chains of fatty acids into the mitochondrial matrix, thus allowing the cells to break down fat and get energy from the stored fat reserves. Recent studies have started to shed light on the beneficial effects of L-carnitine when used in various clinical therapies. Because L-carnitine and its esters help reduce oxidative stress, they have been proposed as a treatment for many conditions, i.e. heart failure, angina and weight loss. For other conditions, such as fatigue or improving exercise performance, L-carnitine appears safe but does not seem to have a significant effect. The presented review of the literature suggests that continued studies are required before L-carnitine administration could be recommended as a routine procedure in the noted disorders. Further research is warranted in order to evaluate the biochemical, pharmacological, and physiological determinants of the response to carnitine supplementation, as well as to determine the potential benefits of carnitine supplements in selected categories of individuals who do not have fatty acid oxidation defects.