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In this chapter, the roles of the macronutrients nitrogen (N), sulfur (S), phosphorus (P), magnesium (Mg), calcium (Ca), and potassium (K) in plant metabolism and growth are described together with the consequences of deficiency and toxicity. After carbon, N is the element required in the largest quantity by plants and is a major driver for crop yield; it plays a central role in plant metabolism as a constituent of proteins, nucleic acids, chlorophyll, coenzymes, phytohormones, and secondary metabolites. After uptake from the environment mostly as ammonium or nitrate, N is assimilated into amino acids in either roots or shoots. Within the plant, N may be translocated as nitrate or amino acids. Sulfur is taken up as sulfate and assimilated into S-containing amino acids such as cysteine which are used to synthesize S-containing enzymes and coenzymes as well as secondary compounds such as phytochelatins …