Olive (Olea europaea L.) is an evergreen tree traditionally cultivated in the Mediterranean basin where plants undergo, to some degree, stress due to unfavourable environmental conditions. Water deficit, freezing, salinity and air pollution are a few of the stress factors restricting growth, so that olive productivity at the end of the growing season expresses only a fraction of the plant's genetic potential. Understanding the physiological and biochemical processes that enable olive adaptation and acclimation, as well as the mechanisms of stress injury, is therefore of relevant importance. However, the studies on the physiology and biochemistry of stress resistance and on the role of gene expression and protein synthesis in olive are almost in an initial phase when compared with the progress achieved for other cultivated plants. In this paper, the physiological and biochemical studies performed on olive plants exposed to the main environmental stresses will be analysed and discussed. (Olea europaea L.) is an evergreen tree traditionally cultivated in the Mediterranean basin where several environmental constraints are limiting factors for its productivity. Water deficit and salinity stresses are probably the main restrictions for olive cultivation in the Mediterranean climate, though olive behaves as an intermediate drought- and salt-tolerant species when compared with other temperate fruit trees. Low (freezing) temperature becomes a stressful factor when olive cultivation areas approach climatic limits, as usually happens in the northern and central Italian regions and also in some southern zones of Europe. In these areas, plant survival can be seriously compromised when temperature approaches -10oC. In the last decades, human activities have increased the number of environmental constraints that cultivated plants have to cope with and atmospheric pollution is probably the main one. Significant changes in the composition of atmosphere have been observed for several gases, such as for tropospheric ozone (O3) and carbon dioxide (CO2). These changes have opened exciting areas for environmental studies and several articles have been published on this subject. However, the effects of O3, and CO2 on olive physiology and biochemistry, especially when considering long-term realistic experiments, are still almost unexplored. Despite the relevant importance of olive resistance to environmental stress, the studies in this field are still limited when compared to the progress achieved in other cultivated species. In this paper, the physiological and biochemical studies performed on olive plants exposed to environmental stress will be analysed and discussed. WATER DEFICIT In Mediterranean climates water deficit is probably one of the main restrictions for olive cultivation, though olive behaves as an intermediate drought-tolerant species when compared with other temperate fruit trees. Olive leaves can, in fact, tolerate very low water potential (up to -6÷8 MPa) and lose almost 40% of tissue water, while maintaining a full rehydration capacity (Rhizopoulou et al. 1991). These adaptations enable olive