Several improvements in ovarian cancer treatment have been achieved in recent years, both in surgeryand in combination chemotherapy with targeting. However, ovarian tumors remain the women’s cancers withhighest mortality rates. In this scenario, a pivotal role has been endorsed to the immunological environmentand to the immunological mechanisms involved in ovarian cancer behavior. Recent evidence suggests a loss ofthe critical balance between immune-activating and immune-suppressing mechanisms when oncogenesis andcancer progression occur. Ovarian cancer generates a mechanism to escape the immune system by producinga highly suppressive environment. Immune-activated tumor infiltrating lymphocytes (TILs) in ovarian tumortissue testify that the immune system is the trigger in this neoplasm. The TIL mileau has been demonstrated tobe associated with better prognosis, more chemosensitivity, and more cases of optimal residual tumor achievedduring primary cytoreduction. Nowadays, scientists are focusing attention on new immunologically effectivetumor biomarkers in order to optimize selection of patients for recruitment in clinical trials and to identifyrelationships of these biomarkers with responses to immunotherapeutics. Assessing this point of view, TILsmight be considered as a potent predictive immunotherapy biomarker.