Primary ovarian insufficiency (POI) is a significant long-term consequence of gonadotoxic cancer treatments, which leads to infertility and systemic health concerns in survivors with ovaries. Ovarian tissue cryopreservation and transplantation (OTCT) is currently the only fertility preservation approach available to prepubertal patients or patients unable to delay cancer therapy, offering the potential to restore both fertility and physiological ovarian endocrine function. Despite promising outcomes, including up to 89% restoration of ovarian endocrine function and over 180 reported live births, OTCT remains limited by variable graft performance and functional longevity. A primary barrier to long-term OTCT success is massive primordial follicle loss following transplantation, driven largely by delayed graft revascularization and ensuing ischemic and reperfusion injuries. This chapter reviews the clinical background of OTCT, including tissue sources, transplantation sites, and current limitations. Special emphasis is placed on the mechanisms by which delayed revascularization induces ischemia, oxidative stress, follicle apoptosis, and abnormal follicle activation that collectively curtail graft function. The chapter then explores biomaterial strategies that enhance revascularization and follicle survival in preclinical human ovarian xenograft models, followed by emerging biomaterial systems from broader tissue engineering applications that inform the design and clinical translation of future OTCT approaches.