This document discusses the use of organoid cultures in cancer research. It begins with an overview of what organoids are and provides a simple definition of organoids as miniature organs grown in vitro. The document then discusses how three-dimensional culture techniques have enabled the real-time study of mammalian tissues by allowing independent manipulation of genetic and microenvironmental factors. Examples are provided of different cellular inputs used in 3D cultures as well as different culture formats. The roles of 3D cultures in advancing cancer therapeutics through predictive and prognostic testing of preclinical treatments are also summarized.