Since the initial identification of microRNAs (miRNA) in C. elegans, functional characterisation of these small non-coding RNAs has demonstrated their critical involvement in numerous biological processes. Typically 20-22 nucleotides in length, miRNAs act as negative gene regulators at the post-transcriptional level. A large body of evidence points to the role of miRNAs in haematopoiesis. miRNAs provide a network of signals important for haematopoietic cell maintenance, lineage differentiation and cell maturation. The mechanism by which they mediate their effects in haematopoiesis is complex, demonstrating cell-specific, tissue-specific and maturation-specific expression. Understanding haematopoietic expression and key targets of miRNAs is important to further elucidate the functional roles of miRNAs. Furthermore, an appreciation of their role in normal physiological processes sheds light on the possibility that aberrations of miRNA expression may perturb these processes and cause disease. Indeed, deregulation of miRNAs has been demonstrated in oncogenesis and in haematological malignancies in particular. This review focuses on miRNA expression in normal haematopoiesis and provides brief insight into how deregulation of these miRNA may contribute to cancer pathogenesis.