MicroRNAs (miRNAs) are small, noncoding RNAs that regulate protein synthesis posttranscriptionally. Although they were discovered only about 15 years ago, it is now clear that miRNAs participate in the formation and function of virtually all vertebrate tissues. Moreover, dysregulation of miRNAs contributes to numerous diseases, including cancer. Here, we review the field of miRNA biology, emphasizing its impact on erythropoiesis.Genetic disruption of global miRNA synthesis in hematopoietic tissues causes anemia with blocked erythropoiesis. Current research focuses on identifying specific miRNAs and associated genetic pathways that modulate normal and pathological erythroid development. In parallel, new technologies to examine and manipulate miRNAs, both as research tools and as therapeutic targets, are emerging rapidly.The field of miRNA biology is evolving and expanding at a remarkable pace. Continued research into how miRNAs impact erythropoiesis will advance our basic understanding of this process and perhaps provide new insights into diagnosing and treating erythrocyte disorders.