N onsense-mediated mRNA decay (NM D) appears to be widespread in the plant kingdom. Numerous studies have documented a correlation between the presence of premature termination codons (PTCs) and a decrease in mRNA abundance for a variety of genes and in a large number of flowering plants. Examples include the Kunitz trypsin inhibitor gene in soybean, the phytohemagglutinin (PHA) gene in common bean, the waxy gene in rice and wheat, the AUX1 and FAD7 genes mArabidopsis, the Chs gene in petunia, the Xantha-f gene in barley, and the Fed-1 gene in tobacco.1'10 Therefore, NM D appears to be a general feature of not only animals (see chapter by Maquat) and fungi (see chapter by Baker and Parker) but also plants. Animals and fungi diverged from each other after they diverged from plants. Thus, any features in common between plants and either animals or fungi are likely ancestral features. Where animals and fungi differ, plants can provide insight into the evolutionary origin of these differences. In this review we will summarize the evidence for NM D in plants, and will highlight some of the cases where plants provide additional insight not available through studies o f fungi and animals.