The expression of seed storage protein genes is restricted to particular times during development and to particular cells. This chapter discusses the various mechanisms by which this pattern of gene expression is achieved. In addition to organ specificity there is cellular specificity within the seed itself. A positive seed-specific element would stimulate transcription, presumably by interaction with a transcription factor that is abundant and active only in the seed. The observation that seed storage protein genes from legumes and many cereals are expressed correctly in transgenic tobacco and petunia indicates that the transcription factors of the hosts can recognize common cis-acting Deoxyribonucleic acid sequences in the promoters. Many nuclear proteins bind in the 5’ regions of genes encoding legume 7S proteins. Some regions containing protein-binding sites also contain conserved elements and/or have been shown in gene transfer experiments to contain cis-acting elements. Genotype can also influence seed protein levels in peas by posttranscriptional mechanisms.