Control of gene expression is exerted by multiple steps such as transcription, mRNA processing, mRNA export, mRNA degradation, translation, and posttranslational events. Recent discovery of small RNAs has enhanced the impact of posttranscriptional regulation, in particular, alterations in mRNA stability in the regulation of gene expression. Therefore, mRNA turnover is an important process not only for setting the basal level of gene expression but also as a regulatory step. Compared to the mechanism of transcription, much less information is available regarding mRNA degradation machineries. However, in the past several years, various components involved in the mRNA degradation process have been identified in eukaryotes. In particular, progress in the plant field has revealed the involvement of mRNA turnover in a wide variety of developmental processes and hormonal responses. Here, we provide an overview of machineries involved in general mRNA degradation and mRNA surveillance systems in plants.