Importance Globally, 968 350 new cases and 659 853 deaths from gastric cancer were reported in 2022. In the US, 30 300 new cases and 10 780 deaths were estimated in 2025. Observations Gastric cancer is more common in men, and the median age at diagnosis is 68 years. Most gastric cancers (&gt;90%) are adenocarcinomas. Worldwide, 85% of cases arise from the stomach body or antrum and 15% from the cardia. In the US, more than 90% of patients diagnosed with gastric cancer present with symptoms such as weight loss and abdominal pain. At presentation, approximately 13% have localized disease (limited to the stomach), 15% to 25% have locally advanced disease, defined as a tumor that has spread to regional lymph nodes, and 35% to 65% have metastatic disease. Helicobacter pylori infection is a treatable risk factor associated with 90% of gastric body and antrum cancers globally. Additional modifiable risk factors include smoking, alcohol, obesity, and salt intake. In countries with high incidence such as Japan and Korea, routine endoscopic screening beginning at age 40 years is associated with improved survival. Diagnosis is made by endoscopic biopsy. Patients with localized gastric cancer are treated with surgical resection and have a 5-year relative survival rate of 75% with treatment. Patients with more advanced-stage disease should receive gastrectomy, perioperative chemotherapy with 5-fluorouracil, oxaliplatin, and docetaxel and immunotherapy (durvalumab). Metastatic or unresectable disease may be treated with chemotherapy, immunotherapy, and/or targeted therapy depending on biomarkers, including programmed cell death ligand 1 (PD-L1), human epidermal growth factor receptor 2 ( ERBB2 ; formerly HER2 or HER2/neu ), and claudin-18, isoform 2 (CLDN18.2). For PD-L1–expressing gastric cancer, adding immune checkpoint inhibitors, such as nivolumab and pembrolizumab, is associated with an additional 3 months of survival when compared with chemotherapy alone. For gastric cancers overexpressing the ERBB2 or CLDN18.2 proteins, the addition of trastuzumab or zolbetuximab, respectively, is associated with an additional 3 to 4 months’ survival. Early supportive care focusing on symptom management and on nutritional and psychosocial support is associated with 3 months of survival benefit. Less than 10% of patients with metastatic gastric cancer survive more than 5 years. Conclusions and Relevance Approximately 30 300 new cases of gastric cancer are diagnosed annually in the US. Localized gastric cancer is treated with gastrectomy, and locally advanced disease is treated with surgery and chemoimmunotherapy. For patients with unresectable or metastatic gastric cancer, chemotherapy with immune checkpoint inhibitors and targeted therapies such as trastuzumab or zolbetuximab improves survival by several months.