This chapter deals with the mechanisms and regulation of mineral nutrient storage during seed formation. Such stores are found in tiny seeds, such as those of Begonia and orchids, as well as in large seeds, such as walnut. A role for phytin and phytic acid may be in the control of inorganic phosphate homeostasis in both developing seeds and seedlings. The mechanisms by which phytin is synthesized in developing seeds is greatly in need of attention. There are indications that the accumulation of mineral nutrients and storage proteins are interrelated. Perhaps the best method to determine the importance and roles of phytic acid in seeds, and the pathways to, or at least the proteins involved in, phytic acid biosynthesis, is to obtain mutants. Arabidopsis would be a promising system to use, with its small genome, short generation time, ease of mutagenesis, and well known genetics.