Sestrins belong to a family of evolutionary conserved proteins which are found in the majority of animal species. While invertebrate genomes contain only one sestrin gene, mammalian and other vertebrate genomes comprise three highly homologous genes that encode Sestrin 1, 2 and 3 proteins (Sesn1, Sesn2 and Sesn3). Sestrins are activated in response to a variety of stimuli and trigger metabolic shifts promoting cell survival under stress conditions. Although cellular stress within an organism is often caused by external stimuli it can be induced by excess of cytokines, chemokines, reactive oxygen species which are produced during aberrant metabolic or immune processes and are involved in regulation of cell physiological states including cell death. Activation of sestrins facilitates cell adaptation to stress through stimulation of antioxidant response and autophagy through regulation of the signaling pathways mediated by AMPK and mTOR kinases. These activities are involved in protection of the organism during physical exercise and certain level of sestrins activity contributes to the development of age-related diseases. However, prolonged activation of sestrins under chronic stress may cause negative effects for the organism.