 craniofacial reconstruction requires robust bone of specified geometry for the repair to be both functional and aesthetically pleasing. Two main strategies exist for generating such bone, in vitro bioreactors and in vivo bioreactors. In vitro bioreactors use cells harvested from the patient, a scaffold, and a device to increase mass transfer of nutrients, oxygen, and waste, allowing for generation of larger viable tissues. In vivo bioreactors use the patient's own body as a source of cells and of nutrient transfer and involve the implantation of a scaffold with or without growth factors adjacent to vasculature, followed by the eventual transfer of vascularized, mineralized tissue to the defect site. Both types of bioreactors have their advantages and drawbacks, and further research is needed to determine which type of bioreactor is most effective for craniofacial reconstruction. This article was authored by Emma Watson and Antonio's G. Micas.