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Trees grow in a multilayered environment composed of numerous abiotic chemical and physical factors. An excess or deficit in the chemical or physical environment causes stress or negative physiological, biochemical, and structural consequences for trees. Among the environmental factors that cause a reduction in wood formation are nutrient deficiency (especially phosphorus, potassium, calcium, and nitrogen starvation), drought, high or low temperature, and soil salinity. Air pollutants, such as ozone, also can damage plants and affect wood formation of trees. Susceptibility or resistance to the different stress types depends on the species, the genotype, and the age of the tree. Stress cause numerous plant responses, from changes in gene expression to reductions in growth rate, crop yield, and wood formation. The severity and duration at which stress occurs affect the extent of the response of the tree. A combination of different stress types can elicit stronger tree responses than a single type of stress. Stress can trigger a response directly (e.g., by drought) or can induce an injury, such as a damage of the bark by high temperature. The process of response can also enable a tree to acclimate to stress by developing resistance mechanisms. The aim of this chapter is to give a brief overview of the essential stress types affecting wood formation.