Vitamins are a class of molecules that play an essential role in metabolism. In order to enhance or to complete the nutritional value of a food, it is sometimes, necessary to add vitamins during processing. Most vitamins may be produced by chemical synthesis, but the natural sources are both more appealing to the consumer and, sometimes, more bioavailable. Natural and genetically modified microorganisms are a possible alternative to produce vitamins. Another broad class of molecules, nutraceuticals, includes substances which are not essential in diets, but which may have beneficial roles besides that of supplying building blocks, energy, coenzymes and minerals for the body. This chapter presents both the classes of compounds, vitamins and nutraceuticals, their use in processed food, and focuses on the classical and microbial sources of vitamins and then role in the human body, and some representative nutraceuticals. Aminoacids, organic acids, prebiotics, polyunsaturated oils, hydrocolloids, enzymes and other molecules which are bioactive or nutritionally important, but pertinent to other classes of additives, are not discussed in this chapter.