During embryonic development, a precise and tightly regulated hierarchy of gene expression is necessary to ensure the proper formation of all cell types and organs. In all animals and plants,microRNAs play a prominent role in the control of gene expression at the post-transcriptional level. In the last few years,microRNAs have emerged as important players during embryogenesis.As suggested by recent reports, microRNAs regulate crucial developmental processes, such as organizer induction,cell fate determination and body axis formation. In this review,we will discuss the role of microRNAs in early development of vertebrate model systems and in human embryonic stem cells,as an in vitro paradigm for human development.