Ovarian cancer is a challenging disease that nonetheless provokes brisk, prognostically favorable immune responses in many patients. The biology of ovarian cancer offers unique insights into the factors that engender protective tumor immunity. Tumor-infiltrating lymphocyte (TIL) patterns range from CD8+ TIL alone to complex aggregates that additionally include CD4+ and CD20+ TIL. Patient survival rates increase in step with TIL complexity, suggesting cooperative interactions between these lymphocyte subsets. TIL are associated with high-grade serous histology and BRCA1 disruption; the latter may promote immunity through altered cytokine signaling, oxidative stress responses, or antigen expression. The ovarian tumor genome demonstrates extensive spatial and temporal heterogeneity, yet TIL exhibit relatively homogeneous spatial distributions that may reflect core properties of the tumor. In summary, ovarian cancer attracts the attention of the immune system in ways that create unique challenges and opportunities for immunotherapy.