Mineral deficiency stress is caused by the deficiency of essential nutritional elements in the plant. This chapter opens on the grounds that essential elements in plant nutrition are required in the plant at optimal concentrations, and that any departure from the required concentrations causes plant stress that often takes the form of what is recognized as mineral deficiency symptoms and/or reduced growth and yield. Mineral-toxicity stress involves plant reactions to toxic concentrations of any available mineral in the rhizosphere. Acidic soils that contain toxic concentrations of aluminum and manganese may be regarded as the most important problem of mineral toxicity in agriculture, as they are estimated to comprise about 40% of the arable land world-wide. Resistance to various metals common to contaminated sites is often performed by planting the materials in the problem site. This is a simple and reasonable approach, as often each specific contaminated site is the breeding target environment.