Natural low-calorie sweeteners have received renewed attention with the toxicological acceptance and commercial development of steviol glycosides in the West. Excluding the simple sugars and polyols, there are 100 or more sweet compounds found in nature. However, the majority of these have little prospect of becoming commercial ingredients because they fail to meet one or more key criteria for commercial success. This chapter concentrates on the small number of natural, low-calorie sweeteners that either are, or are likely to become, commercially successful. Others that may be encountered in the literature are mentioned briefly for completeness.