永生細胞系，是指一組在多細胞生命中的細胞群，因為基因突變，已經逃避了正常的細胞衰老，而是可以繼續進行分裂，甚至無限無止境地繁殖，細胞可以在體外長時間生長。
永生細胞系，可以來自自然發生的突變，例如癌細胞。也可以出於實驗目的有意誘導。 永生細胞係是研究多細胞生物的生物化學和細胞生物學的非常重要的工具。
永生細胞系也用於生物技術。值得留意的是，幹細胞雖然可以不斷分裂繁殖，但不屬永生細胞系。
目前著名的永生細胞系包括海拉細胞。[1][2][3][4][5][6]
Skloot, Rebecca. Henrietta's Dance. Johns Hopkins Magazine. [5 April 2021]. （原始內容存檔於2021-11-30）. Isolation from a naturally occurring cancer. This is the original method for generating an immortalised cell line. Major examples include human HeLa, the line is derived from cervical cancer cells taken on February 8, 1951 from Henrietta Lacks, a 31-year-old African-American mother of five, who died of cancer on October 4, 1951.
Henle W, Henle G. Epidemiologic aspects of Epstein-Barr virus (EBV)-associated diseases. Annals of the New York Academy of Sciences. 1980, 354: 326–31. PMID 6261650. S2CID 30025994. doi:10.1111/j.1749-6632.1980.tb27975.x. Introduction of a viral gene that partially deregulates the cell cycle (e.g., the adenovirus type 5 E1 gene was used to immortalise the HEK 293 cell line; the Epstein-Barr virus can immortalise B lymphocytes by infection
