Life is ubiquitous on Earth wherever liquid water is present. The three domains of life Eukaryota, Bacteria, and Archaea, although very different, have a common origin. They share the basic enzymatic machinery, and they use ATP as an energy source. Every organism is adapted to a specific set of environmental conditions. Divergence from such conditions disturbs the normal functioning of the organism and generates stress - a pressure to adapt to the new conditions. Stress can be caused by many factors, from lack of nutrients to heat, cold, radiation, and toxins. Organism’s reaction to stress is called stress response. It involves modification of cellular functioning, which may include activation of specific transcriptional programs, modification of membranes and proteins, production of protective compounds, and metabolic adaptations. Every type of stress causes similar problems in all organisms; for example, heat causes protein denaturation. A universal response to this problem is the production of chaperones that help proteins to refold and of other compounds that stabilize protein structure. Accordingly, diverse organisms share many features of their stress responses.