The concept of cancer stem cells (CSC) has drawn great attention from researchers in both molecular and clinical fields as has brought a new perspective to the way we manage cancer. CSC have several characteristics that are shared by the properties of normal stem cells, such as differentiation, self-renewal and homeostatic control. However, CSC have the capacity to both divide and expand the CSC pool and to differentiate into heterogeneous non-tumorigenic cancer cells. Even more, CSC have an inherent high resistance to chemotherapeutic agents that leads to recurrence and poor long-term survival, especially in lung cancer patients. CSC-targeting agents are now undergoing in vitro and in vivo studies, some of which have provided promising results for further clinical studies setting. In this article we review the concept of CSC from the perspective of tumor biology, including the origin of CSC and its biomarkers. As lung cancer is the leading cause of cancer-related deaths worldwide, we focus on the properties and clinical implications of lung CSC.