Cancer is a major health problem and a leading cause of death worldwide. Early cancer detection and continuous changes in treatment strategies have improved overall patient survival. The recent development of targeted drugs offers new opportunities for personalized cancer treatment. Nevertheless, individualized treatment is accompanied by the need for biomarkers predicting the response of a patient to a certain drug. One of the most promising breakthroughs in recent years that might help to overcome this problem is the organoid technology. Organoid cultures exhibit self-renewal capacity, self-organization, and long-term proliferation, while recapitulating many aspects of their primary tissue. Generated patient-derived organoid (PDO) libraries constitute "living" biobanks, allowing the in-depth analysis of tissue function, development, tumor initiation, and cancer pathobiology. Organoids can be derived from all gastrointestinal tissues, including esophageal, gastric, liver, pancreatic, small intestinal and colorectal tissues, and cancers of these tissues. PDOs are amenable to various techniques, including sequencing analyses, drug screening, targeted therapy testing, tumor microenvironment studies, and genetic engineering capabilities. In this review, we discuss the different applications of gastrointestinal organoids in basic cancer biology and clinical translation.Cancer: personalized models of gastrointestinal tumors Three-dimensional mini-organs or "organoids" derived from patients with gastrointestinal tumors can offer new insights into cancer biology and guide the selection of appropriate therapies. By cultivating gastrointestinal tumor cells with an appropriate combination of growth factors, researchers can generate organoids that recapitulate key features of the original malignancy in miniature. Therese Seidlitz and Daniel E. Stange from the University Hospital Carl Gustav Carus in Dresden, Germany have reviewed the use of such models for cancer research and clinical care. These organoids can be used to identify the treatment strategies most likely to be effective in a given patient, or to assess differences between primary tumors and their metastases. Researchers can also genetically manipulate organoids made from healthy tissue to study the biological pathways that contribute to tumor development and disease progression in cancer patients.