Immunotherapy has revolutionized cancer treatment and the management of autoimmune diseases by harnessing the body's immune system. Checkpoint inhibitors, CAR-T cell therapy, and cancer vaccines have shown remarkable success, particularly in melanoma, hematologic malignancies, and some solid tumors. However, challenges remain, including variable patient responses, immune-related adverse events, and resistance mechanisms. Future research aims to enhance efficacy through combination therapies (e.g., with targeted agents or radiotherapy), novel biomarkers for patient stratification, and next-generation engineered immune cells (e.g., dual-targeting CAR-T, NK cell therapies). Additionally, advances in microbiome modulation, personalized neoantigen vaccines, and AI-driven drug design hold promise. Beyond oncology, immunotherapy is being explored for neurodegenerative, infectious, and inflammatory diseases. Overcoming toxicity, improving tumor microenvironment targeting, and expanding accessibility will be critical for the next decade of progress.