Immune checkpoint inhibitors are a class of drugs that act on immune checkpoints (the three major ones being CTLA4, PD-1, and PD-L1) and are novel treatment options for cancer. The clinical applications discussed with respect to malignant melanoma, urothelial carcinoma, non-small cell lung cancer, head and neck and esophageal squamous cell carcinoma, and haematological malignancies shed light on the various uses of the immune checkpoint inhibitors in cancer therapy. However, since these are a relatively new class of drugs with special mechanisms of action, severe side effects may manifest in the majority of the patients. This can be remedied by the usage of the immune checkpoint inhibitors in combination with each other, which has been shown to have better tolerability. Further improvement of this novel class of drugs is ensured by constant research and experimentation, which has led to the rise of the new generations of immune checkpoint inhibitors that act on other immune checkpoints such as TIM-3, LAG-3, GITR, and CD40.