Although more difficult to control and engineer than the usually monogenic traits of resistance to biotic pests and herbicides, the genetically-complex response to abiotic stress conditions, such as drought, salinity, extreme temperatures, chemical toxicity and oxidative stress, is globally and regionally far more important. Drought and salinization, usually manifested as osmotic stress, are the most serious threats to agriculture and to maintaining a safe environment in many parts of the world. Abiotic stress is expressed in plants by a series of morphological, physiological, biochemical and molecular changes that adversely affect plant growth and productivity. The major interacting domains of stress tolerance include whole plant and cell physiology, molecular biology, genetics, and breeding. The use of molecular tools for elucidating the molecular control mechanisms of osmotic stress tolerance, and for engineering more tolerant plants is based on the expression of specific stress-related genes. These genes regulate osmoprotection, water and ion movements, a variety of functional and structural stress-induced proteins, signal perception and transduction, free radical scavenging, and many others. The role of a number of molecular mechanisms associated with osmotic stress tolerance in plants will be reviewed. In addition to few other mechanisms, the characteristics, expression, regulation and possible function(s) of one of these proteins/genes, the boiling-stable protein BspA that was isolated from Populus tremula, will be presented and assessed. Finally, the potential contribution of biotechnology to abiotic stress tolerance will be discussed.