Regulation of gene expression is a multidimensional process. In prokaryotes, the regulation is mostly, but not wholly, at the transcriptional level. As complex organisms evolved, the complexity and diversity of regulatory mechanisms also grew in parallel. In eukaryotes, particularly in metazoans, posttranscriptional regulation of gene expression has assumed many dimensions. As soon as the mRNA synthesis starts, several co-transcriptional processes initiate. These processes include regulation involving capping, alternative splicing, mRNA modifications, and alternative 3′-polyadenylation. These regulatory processes control the quality of the mRNA, selective export of mRNA for translation, and other phenomena that lead to modulation of the composition of the proteome, as well as concentrations of target proteins. Once exported to the cytoplasm, translational control ensures that the proper mRNA is translated. Translation is subject to many regulatory processes to respond to external and internal stresses. Posttranslation, chemical modifications, and regulated degradation alter the proteome and, hence, the biology of the cell. These regulatory processes are explored in this chapter, focusing on eukaryotes.