MicroRNAs (miRNAs) are a family of 19- to 24-nucleotide noncoding RNAs that regulate messenger RNA function at the posttranscriptional and translational level. Recent literature demonstrates a significant role of miRNAs in normal and malignant hematopoiesis. Specific miRNAs have been shown to regulate each step of hematopoiesis starting at the level of multipotent progenitors through terminal stages of myeloid and lymphoid differentiation. Similarly, individual miRNAs and miRNA signatures have been associated with specific hematologic malignancies. There is accumulating evidence that miRNAs can be used for diagnostic, prognostic, and therapeutic purposes. This review highlights the current status of knowledge on miRNA in normal and malignant hematopoiesis.