The rare stable isotope of hydrogen, deuterium, has fascinated researchers since its discovery in the 1930s. Subsequent large-scale production of deuterium oxide, commonly known as heavy water, became a starting point for further research. Deuterium exhibits unique physicochemical properties as well as having the strongest kinetic isotope effects among all other elements. Moreover, a broad variety of morphological and physiological changes have been observed in deuterium-treated cells and organisms, including changes in fundamental processes such as cell division or energy metabolism. Even though our understanding of such alterations is still insufficient, it is evident that some of them make growth in a deuterium-enriched environment a challenging task. There seems to be certain species-specific limits to their tolerance to heavy water, where some organisms are unable to grow in heavy water whilst others have no difficulties. Although the effects of deuterium on living organisms are, in general, negative, some of its applications are of great biotechnological potential, as is the case of stable isotope-labelled compounds or deuterated drugs.