Immune surveillance mechanisms are essential for the identification and elimination of altered cells that, left unchecked, may give rise to cancer. The study of these mechanisms has been focused particularly on antigen-specific anti-tumor responses that involve adaptive T and B cells, with the involvement of innate cells circumscribed mostly to the cytotoxic natural killer cell population. Nevertheless, advances in the study of leukocyte phenotypes and functions have discovered an important variety of innate lymphoid cell populations with multiple roles in both physiologic and pathologic conditions, including lymphoid tissue-inducer; helper-like type 1, 2, and 3 innate lymphoid cells; NKT; and Tγδ cells. Recent studies have explored the relevance of these cell populations in cancer pathogenesis, shedding light on their importance for tissue homeostasis and repair, as well as for the activation and modulation of anti-tumor immune responses. Innate lymphoid cells have been found to possess potent anti-tumor effects under specific conditions, either through direct cytotoxic mechanisms or by production of soluble factors that modulate the effector phenotypes of adaptive immune cells. Recent studies demonstrate that innate lymphoid cells are susceptible to clinical manipulation and provide significant benefits for therapeutic intervention in cancer patients. The present chapter presents information on the significant role of innate lymphoid cells in cancer development and evolution.