The discovery that regulatory RNAs control almost every biological pathway has revolutionized our understanding of gene expression. At the forefront, microRNAs (miRNAs) have proven to be an abundant and essential class of RNA molecules in plants and animals. The numerous examples of defects in specific miRNA pathways contributing to complex diseases, including cancer, heart ailments and neuronal pathologies highlight the importance of these regulatory RNAs in human biology. The overall goal of the Pasquinelli Lab research program is to understand how miRNA-mediated regulation of gene expression contributes to organismal development and viability. We have primarily used C. elegans as a model animal system to investigate how miRNAs are expressed and regulate gene expression in an endogenous context. The pathways we study are broadly conserved throughout animal phylogeny and relevant to understanding the role of miRNAs in human development and disease.