Organoids are three-dimensional culture systems generated from embryonic stem cells, induced pluripotent stem cells, and adult stem cells. They are capable of cell proliferation, differentiation, and self-renewal. Upon stimulation by signal factors and/or growth factors, organoids self-assemble to replicate the morphological and structural characteristics of the corresponding organs. They provide an extraordinary platform for investigating organ development and mimicking pathological processes. Organoid biobanks derived from a wide range of carcinomas have been established to represent different lesions or stages of clinical tumors. Importantly, genomic and transcriptomic analyses have confirmed maintenance of intra- and interpatient heterogeneities in organoids. Therefore, this technology has the potential to revolutionize drug screening and personalized medicine. In this review, we summarized the characteristics and applications of organoids in cancer research by the establishment of organoid biobanks directly from tumor organoids or from genetically modified non-cancerous organoids. We also analyzed the current state of organoid applications in drug screening and personalized medicine.