Claudin 18.2 (CLDN18.2), a tight junction protein selectively expressed in normal gastric epithelium and widely retained during carcinogenesis, has emerged as a promising therapeutic target for advanced gastric cancer (AGC). SPOTLIGHT and GLOW trials evaluated the anti-CLDN18.2 monoclonal antibody (mAb) zolbetuximab in combination with first-line chemotherapy, and established CLDN18.2 as a therapeutic target, initiating a paradigm shift toward a biomarker-driven treatment approach in AGC. In addition, from zolbetuximab to a diverse pipeline of promising high-affinity mAbs, bispecific antibodies, antibody-drug conjugates and chimeric antigen receptor T cells, this target has established a new and highly effective therapeutic avenue for CLDN18.2-expressing AGC. Therefore, as research progresses, CLDN18.2-targeted therapy is poised to become a cornerstone of treatment across multiple disease stages and cancer types. This review describes the biological role of CLDN18.2 in normal gastric epithelium and gastric carcinogenesis and summarizes the current therapeutic landscape and future perspectives targeting CLDN18.2 in AGC.