AbstractTrypanosomatids are unicellular eukaryotes responsible for severe diseases in humans. They exhibit a number of remarkable biological phenomena, especially at the RNA level. During their life cycles, they alternate between a mammalian host and an insect vector and undergo profound biochemical and morphological transformations in order to adapt to the different environments they find within one or the other host species. These changes are orchestrated by specific gene expression programs. In contrast to other organisms, trypanosomatids do not regulate RNA polymerase II‐dependent transcription initiation. Evidence so far indicates that the main control points in gene expression are mRNA degradation and translation. Recent studies have shown that RNA‐binding proteins (RBPs) play a critical role in the developmental regulation of mRNA and protein abundance. RBPs seem to bind to specific subsets of mRNAs encoding functionally related proteins. These ribonucleoprotein complexes may represent posttranscriptional operons or regulons that are able to control the fate of multiple mRNAs simultaneously. We suggest that trypanosomatids transduce environmental signals into mRNA and protein abundance through posttranslational modification of RBPs. Copyright © 2010 John Wiley & Sons, Ltd.This article is categorized under: RNA Interactions with Proteins and Other Molecules > Protein‐RNA Interactions: Functional Implications RNA in Disease and Development > RNA in Disease