To date, few articles have systematically described the applications and advances of CRISPR-Cas9 in cancer immunotherapy. Immunotherapy has emerged as one of the most promising therapeutic strategies in cancer. CRISPR-Cas9 system, as an RNA-guided genome editing technology, can be implemented to fuel the production of therapeutic immune cells such as construction of chimeric antigen receptor T (CAR-T) cells due to its versatility and ease of use. Therefore, in this article, we introduced the historical development and mechanism of CRISPR-Cas9. Also, we focused on its various applications in cancer immunotherapy, particularly in CAR-T cell-based immunotherapy, and discuss the potential challenges it faces in the future, which may attract more attention and provide new insights of CRISPR-Cas9 in cancer immunity. (By An-Liang Xia, https://jmg.bmj.com/content/early/2018/07/03/jmedgenet-2018-105422)