Small cell lung cancer (SCLC) accounts for about 15% of all lung cancer cases and is characterized by an aggressive disease course and a particularly poor prognosis. For decades, the best available systemic therapy for patients with extensive-stage (ES) SCLC consisted of platinum-etoposide chemotherapy. In recent years, however, extensive-stage (ES) SCLC has become the second thoracic malignancy in which immune checkpoint inhibition (ICI) proved to prolong the survival of patients. In fact, the phase III CASPIAN and IMpower133 studies showed that the addition of respectively durvalumab and atezolizumab to chemotherapy significantly prolongs the overall survival (OS) of patients with ES-SCLC. The results of these studies quickly established chemo-immunotherapy as the preferred initial treatment for these patients. Nevertheless, the benefit provided by ICI remains to be limited to a proportion of patients and most patients eventually relapse. Therefore, innovative treatment strategies and ICI-based combinations are currently under investigation to further improve the prognosis of patients with ES-SCLC. In addition, studies are looking into the potential of ICI in patients with limited stage (LS) disease.