Cancer stem cells (CSCs) maintain tumor propagation and heterogeneity due to their capacities of self-renewal and plasticity. Given that the CSCs are responsible for tumor formation, metastasis, drug resistance and relapse, the hypothesis of CSCs has been gradually accepted by more and more tumor researchers. Therefore, it is of great scientific and clinical significance to investigate CSC biology. The CSCs reside in niches (CSC niches), which are part of tumor microenvironments, containing cell-cell contact and secretory factors. Cancer non-stem cells and CSCs themselves also serve as the CSC niches. CSC niches maintain the plasticity of CSCs, protect CSCs from attack by the immune system, and promote tumor metastasis as well. The remodeling of CSC niches by CSCs, the influence of CSC self-renewal by CSC niches, and CSC niche-based targeted interventions emerge as fronts of CSC biology. In this review, we summarize recent progresses on CSC discovery, CSC self-renewal regulation, CSC niches, as well as targeted interventions against CSCs and CSC niches.