Abstract: Three-dimensional organoid technology has remarkably improved with enhanced efficiency in developing organoids from both normal and malignant tissues of patients over the past decade. Patient-derived tumor organoids (PDOs) retain the physiopathological and genetic characteristics of the tumor while providing a high level of patient-specific tumor heterogeneity. PDOs shed light on crucial scientific topics, including the relationship between infectious pathogens or genetic/epigenetic alterations and tumorigenesis, the mechanism of drug resistance, and the prediction of the patient response to specific treatments. With the establishment of tumor organoids and cellular components of the tumor microenvironment, such as immune cell co-culture systems, this technique is now utilized in the rapidly growing field of immuno-oncology. This review discusses the current achievements, applications, and challenges of organoid technology in cancer precision medicine.