Scientists have tried for many years to understand cancer development and progression in the expectation of defining the therapeutic target. Emerging evidence has revealed that cancers contain a minority population, termed “Cancer stem cells (CSCs)”, which are responsible for sustaining the tumour as well as giving rise to proliferating cells. CSCs are thought share the three features with normal stem cells: self-renewal, the capability give rise to multiple lineages, the potential to proliferate extensively and therefore it has been proposed that they have their origin in normal stem cells. However, since there is evidence that genetic alterations occurring in committed progenitor cells can reactive their proliferative potential, the origin of CSCs still remains undecided. In this review, we discuss the current status of cancer stem cells in various tissues, the origin of some cancers from normal stem cells, the evidence for the existence of particular markers and aspects of their cell biology. Better understanding of the relation between adult stem cells and cancer stem cells in tumourigenesis may will provide novel therapeutic strategies against cancers.