Publisher Summary This chapter reviews the evidence for localized mRNAs in eggs and the possibility that mRNA localization may be mediated by the egg cytoskeleton. New methods are developed to determine the spatial distribution of mRNA in cells. The application of these methods can be localized to particular cytoplasmic regions in both somatic cells and eggs. The eggs of diverse groups of animals—including annelids, insects, ascidians, and amphibians—show both general and specific mRNA localizations. Thus, mRNA localization is a widespread phenomenon and may have appeared early during the evolution of metazoans. Some specific localized mRNAs—such as bcd mRNA in Drosophila eggs and Vg-1 mRNA in Xenopus eggs—have an important role in development. Part of the mRNA localization mechanism involves the regional degradation of mRNA. Some egg mRNAs are localized because the proteins they encode are assembled into localized structures during translation. If this is so, it would be expected that inhibiting protein synthesis would disrupt this type of mRNA localization. The egg cytoskeleton is also involved in mRNA localization.