Abstract: Posttranscriptional controls play important roles in the determination of gene expression. A major component of the regulation of gene expression is exerted at the level of mRNA stability. mRNAs can differ dramatically in their intrinsic stabilities. Eukaryotic mRNAs have a considerable range of half–lives, from as short as few minutes to as long as several days. In parallel, specific mRNA decay pathways may also occur to control the quality of mRNA prior to translation. Nonsense–mediated mRNA decay (NMD) is an example of a posttranscriptional mechanism that is used by cells to survey mRNA quality. By degrading abnormal transcripts that prematurely terminate translation, NMD prevents the production of truncated proteins that could have a dominant–negative effect for the cell. Thus, the stability of individual mRNAs reflects the interaction of general determinants with mRNA–specific sequence elements and trans–acting proteins that function to dictate mRNA turnover. In this review, we present the major current conceived mechanisms that specify the stability of the normal human β–globin mRNA, as well as the surveillance mechanism of nonsense–mediated mRNA decay, emphasizing aspects specific for this transcript.