Advanced gastric cancer (AGC) is characterized by high mortality. The survival is estimated as 14.2 months. The treatment of choice in the early stages of GC is surgery. Due to high potential of malignancy, postoperative chemotherapy is usually administered. Novel methods of treatment involve immunotherapeutic agents (IA). The new therapies seem to be a hopeful perspective for patients with advanced GC. In this review, we present the outcomes of clinical trials in GC treatment with IA and their mechanisms of action. Furthermore, we present the benefits and shortcomings of immunotherapy and describe potential directions for future research.