Fatty acids have been part of the biosphere from its beginning, providing a high-calorie foodstuff in metabolism, the structural basis of membranes, an important class of intra- and extracellular signaling molecules, and many other functions. They are a diverse group of molecules, although most are linear aliphatic molecules with a terminal carboxylic acid. Here, we provide an overview of the major classes of fatty acids, their nomenclature, their synthesis, and their biodegradation.