DNA methyltransferase inhibitors, so-called hypomethylating agents (HMAs), are the only drugs approved for the treatment of higher-risk myelodysplastic syndromes and are widely used in this context. However, it is still unclear why some patients respond to HMAs, whereas others do not. Recent sequencing efforts have identified molecular disease entities that may be specifically sensitive to these drugs, and many attempts are being made to clarify how HMAs affect the malignant clone during treatment. Here, we review the most recent data on the clinical effects of HMAs in myeloid malignancies.