The immune system prevents establishment and progression of cancer through innate and adaptive surveillance. However, some cancerous cells successfully evade the immune system. Regulatory T-cells (Tregs) facilitate such evasion. Tregs may be the factor responsible for the limited success of human tumor immunotherapy to date. To improve immunotherapy, it is thought that the number of Tregs and their functions should be inhibited in patients with advanced cancer. In this review, we focus on recent immunotherapy efforts targeting Tregs.