Polyadenylation is an essential processing step for most eukaryotic mRNAs. In the nucleus, poly(A) polymerase adds poly(A) tails to mRNA 3′ ends, contributing to their export, stability and translatability. Recently, a novel class of non‐canonical poly(A) polymerases was discovered in yeast, worms and vertebrates. Different members of the Cid1 family, named after its founding member in the fission yeast Schizosaccharomyces pombe, are localized in the nucleus and the cytoplasm and are thought to target specific RNAs for polyadenylation. Polyadenylation of a target RNA by a Cid1‐like poly(A) polymerase can lead to its degradation or stabilization, depending on the enzyme involved. Cid1‐like proteins have important roles in diverse biological processes, including RNA surveillance pathways, DNA integrity checkpoint responses and RNAi‐dependent heterochromatin formation. Copyright © 2006 John Wiley & Sons, Ltd.