A fission reactor-based neutron irradiation facility was first used for boron neutron capture therapy (BNCT) in 1951 at the Brookhaven Graphite Research Reactor (BGRR). Over the following decades to the present day, 17 research reactors have been used for clinical applications of BNCT and over 50 reactors utilised for all radiation-related aspects of BNCT research. This chapter presents the technical and engineering requirements to design a BNCT facility located in a research reactor environment. The overview is intended to give those who are interested in establishing this type of facility some perspective and guidance concerning the desirable performance characteristics and features. Existing reactor-based neutron irradiation facilities possess many of the features of modern radiotherapy machines and employ modular designs to enable beam line modifications. Nearly all of these requirements are applicable to accelerator-based BNCT facilities.