〔Abstract〕 Inhibitor of DNA binding 1 (ID1) is a crucial regulator of cell differentiation and plays a significant role in maintaining normal hematopoietic differentiation and development. Due to the lack of DNA-binding motif, ID1 functions as a dominant-negative inhibitor of basic helix-loop-helix factors to antagonize their abilities to bind to DNA and transcriptionally regulate target genes. Abnormal expression of ID1 is strongly associated with various hematologic disorders, including myeloid and lymphoblastic leukemia, multiple myeloma and myeloproliferative neoplasms. ID1 acts as a potential oncogene by participating in multiple signaling pathways that promote the malignant proliferation, invasion and therapy resistance in leukemic cells. Significant strides have yielded promising antileukemic effects of ID1 inhibitors, both alone and in combination with targeted therapies against oncogenic signaling pathways. Here, we review the relationship between ID1 expression and the initiation and progression of blood disorders, and summarize the clinical significance of ID1 as a novel therapeutic target and potential prognostic biomarker for hematologic malignancies.