The objective of the present investigation was to conduct a systematic review of empirical studies that have reported the use of identity fusion theory. The review followed guidelines and recommendations of the PRISMA statement. The following databases were used Web of Science, Scopus, ProQuest, ScienceDirect, Willey Online Library, EBSCO and JSTORE databases. Empirical studies were selected, in Spanish and English that were published between 2009 and 2018. 52 articles were found that met the selection criteria. Most studies give evidence that identity fusion is a strong predictor of extreme sacrifice behaviors by the group. Likewise, identity fusion has generally been associated with variables such as: identification with the group, group commitment, perceived social support, loyalty even in ostracized conditions, feelings, affects and emotions towards the group, perception of kinship, among other. Its implications and limitations are discussed.