Tumor organoids are 3D cultures of cancer cells that can be derived on an individual patient basis with a high success rate. This creates opportunities to build large biobanks with relevant patient material that can be used to perform drug screens and facilitate drug development. The high take rate will also allow side-by-side comparison to evaluate the translational potential of this model system to the patient. These tumors-in-a-dish can be established for a variety of tumor types including colorectal, pancreas, stomach, prostate, and breast cancers. In this review, we highlight what is currently known about tumor organoid culture, the advantages and challenges of the model system, compare it with other pre-clinical cancer models, and evaluate its value for drug development. Weeber and Ooft et al. reviewed the current literature on tumor organoid cultures and highlight what is presently known, the advantages and challenges of the system, and the relevance of this pre-clinical cancer model in the context of drug development.