Human embryonic stem cells (hESCs) and induced pluripotent stem cells (iPSCs) reprogrammed from somatic cells can self-renew while maintaining their pluripotency to differentiate into virtually all cell types. In addition to their potential for regenerative medicine, hESCs and iPSCs can also serve as excellent in vitro models for the study of human organogenesis and disease models, as well as drug toxicity screening. MicroRNAs (miRNAs) are nonencoding RNAs of ∼22 nucleotides that function as negative transcriptional regulators via degradation or inhibition by RNA interference (RNAi). MiRNAs play essential roles in developmental pathways. This chapter provides a description of how miRNAs can be introduced into hESCs/iPSCs or their derivatives for experiments via lentivirus-mediated gene transfer.