Bioreactors are a broad category of devices used in the areas of bioprocessing and tissue engineering/regenerative medicine to improve, refine, or optimize a biological process. This definition seeks to encompass the use of the term ‘bioreactor’ for three distinct applications, as used in: producing biologic end-products (production bioreactor); cell or stem cell expansion (cell bioreactor); and tissue engineering (tissue bioreactor).Of these three subtypes of the term ‘bioreactor,’ the production bioreactor is the most widespread and established in terms of industrial solutions available. Yet in the context of biomaterials and tissue engineering, the cell bioreactor and tissue bioreactor are of greater relevance, and in many respects they have little in common with production bioreactors other than the name. The lack of clear terminology frequently leads to confusion, especially in the case of tissue bioreactors, with scientists being deceived into believing that a production or cell bioreactor will be suitable for an application requiring a tissue bioreactor. This article highlights some of the characteristics of each type to aid in the design, selection, and implementation of bioreactor technologies for the application in question. The bioreactors used in tissue engineering can be categorized into two main groups: stirred tank bioreactors where cells or cell aggregates can move in an excess of media and perfusion bioreactors in which cells are immobilized in a reactor core and media is flowed past them. Here, emphasis will be placed on the advantages of perfusion over static culture and the use of bioreactors in culturing stem cells, especially hematopoietic stem cells (HSC) and liver cells. In each case the need for large-scale cell culturing will be described and the experience with bioreactors reviewed. Finally, the concept of the stem cell niche will be considered in the context of core materials for larger bioreactors.