Post-Transcriptional Regulation (PTR) is a key layer of regulation between an organism’s genotype and its functional phenotype. PTR is predominately regulated by (1) the formation of various ribonucleoprotein (RNP) complexes, with RNA binding proteins (RBP) at their core, that repress or calibrate the rate of translation of the messenger RNA; and (2) the splicing and silencing of mRNAs through noncoding RNAs, the spliceosome and RNAi machinery. As such, understanding PTR requires a complex and tiered experimental approach to identify the function and context of each control mechanism, and the specific effectors of regulation in any given circumstance. Giardia duodenalis is a major global parasite that causes diarrhoeal disease in more than 200 million people each year. Understanding PTR in this parasite provides insight into how it establishes infection, interacts with the host and develops drug resistance. In addition, as an early-branching eukaryote, Giardia provides a model to explore and understand the evolution of PTR mechanisms in the Eukaryota, and represents one of the earliest known species to evolve Pumillio domain (Puf) RNA-binding proteins, which are one of the primary classes of translational repression RBPs in higher eukaryotes. Our study aims to identify the RBP repertoire of Giardia. We have bioinformatically curated the currently undefined ‘RBPome’ of Giardia duodenalis and analysed their differential transcription during development \and in response to external stress conditions. In addition, we have used a recently developed interactome capture method (Castello et al; 2012) to pull-down and characterize (by LC-MS/MS) proteins bound to poly-A mRNAs in the parasite’s replicating stage (the trophozoite) in in vitro culture, the first characterization of this kind in any parasitic protist.