Small cell lung cancer (SCLC) is an aggressive malignancy accounting for 15% of all diagnosed cases of lung cancer. For almost two decades there have been no clinically relevant therapeutic advances for this disease. In recent years, however, extensive-stage (ES) SCLC has become the second thoracic malignancy in which immune checkpoint inhibition (ICI) has caused a dramatic therapeutic shift. Today, combinations of platinumetoposide chemotherapy with durvalumab or atezolizumab are considered standard of care in the first line treatment of patients with ES-SCLC. This article will summarize the clinical basis for this paradigm shift and will discuss some clinical challenges that remain with ICI in the treatment of ES-SCLC.