Limitations associated with the study of cancer biology in vitro, including a lack of extracellular matrix, have prompted an interest in analysing the behaviour of tumour cells in a three-dimensional environment. Such model systems can be used to better understand malignancy and metastasis and a cancer's response to therapies. We review the materials that have been used in such models to date, including their fabrication techniques and the results from their study in cancer. Despite the variety of materials available, obstacles remain to perfecting an in vitro model system and we outline some of the challenges yet to be overcome.