Hypoxia (low O2) is a fundamental microenvironmental determinant of bone marrow (BM) pathophysiology. Recent data from molecular and clinical studies indicate that hematopoiesis and leukemogenesis are dependent upon hypoxia-inducible factors (HIFs), a family of essential transcriptional activators mediating the metazoan hypoxic response. In blood cancers, the synergism between HIF overexpression and stabilization within the hypoxic BM microenvironment promotes disease progression, therapy resistance and relapse. In this review, we will summarize current advances in the understanding of HIF signaling in blood cancers and its translational implications for hypoxic-targeted therapy.