The generation of autologous T cells expressing a chimeric antigen receptor (CAR) have revolutionized the field of adoptive cellular therapy. CAR-T cells directed against CD19 have resulted in remarkable clinical responses in patients affected by B-lymphoid malignancies. However, the production of allogeneic CAR-T cells products remains expensive and clinically challenging. Moreover, the toxicity profile of CAR T-cells means that currently these life-saving treatments are only delivered in specialized centers. Therefore, efforts are underway to develop reliable off-the-shelf cellular products with acceptable safety profiles for the treatment of patients with cancer. Natural killer (NK) cells are innate effector lymphocytes with potent antitumor activity. The availability of NK cells from multiple sources and their proven safety profile in the allogeneic setting positions them as attractive contenders for cancer immunotherapy. In this review, we discuss advantages and potential drawbacks of using NK cells as a novel cellular therapy against hematologic malignancies, as well as strategies to further enhance their effector function.