Cyclin B1 is a crucial regulatory protein involved in the cell cycle, particularly in controlling the G2/M transition phase. It forms transiently active kinase complexes with CDK1 (Cyclin-dependent kinase 1) that play distinct roles in mitosis. It accumulates during S-G2, shuttles between the cytoplasm and nucleus, and becomes concentrated in the nucleus in late G2. During prometaphase, Cyclin B1 localizes to centrosomes, mitotic spindle, and chromosomes. Cyclin B1 is involved in the attachment of kinetochore fibers (k-fibers) formed by microtubules during mitosis. It is degraded after the completion of microtubule attachment to kinetochores during mitosis and inactivation of the spindle assembly checkpoint. Uncontrolled expression of Cyclin B1 is associated with neoplastic transformation and the development of gynecological cancers. It has been implicated in the progression of various types of cancer, including gastric, breast, and non-small cell lung cancer. Elevated Cyclin B1 expression correlates with decreased overall survival in multiple cancer types. Cyclin B1/CDK1 is also involved in mitochondrial bioenergetics, which plays a pivotal role in tumor radiation response and resistance to anti-cancer therapies.