In a sequential number of IOP funded research projects the suitability of very specific but otherwise harmless bacteria are tested for their ability to repair cracks significantly improving the durability of concrete structures. Such a bacterial repair mechanism would be beneficial for the economy and the environment at the same time, as concrete is worldwide the most applied building material. This new type of ‘bio-concrete’ or ‘bacteria-based concrete’ could make costly manual repair unnecessary resulting in minimizing the use of raw materials, as structures will last much longer. In nature a huge number of different varieties of bacteria occur and some of these are well adapted to artificial man-made environments such as concrete. From a human perspective concrete may seem an extreme environment as the material is dry and rock-solid. However, this does not apply to a specialized group of bacteria, the ‘extremophiles’, named after their habit to love extreme conditions. Some of these bacterial species are not only known to love extremely dry conditions, but also to be able to produce copious amounts of limestone particularly under alkaline conditions. Limestone is from a physico-chemical viewpoint a concrete compatible material and therefore ideally suitable for durable repair of cracks in concrete. In a series of TU Delft based research projects three types of bacteria-based self-healing concrete products have been developed: 1. Self-healing concrete, 2. Self-healing repair mortar, and 3. A spray-able liquid repair system. Whereas for the first two products a granular ‘healing agent’ in form of encapsulated bacterial spores and feed is required, encapsulation of healing agent ingredients is not needed in the last product. While the focus in the early stage of the research projects was particularly on isolation of suitable bacteria and development of various forms of healing agents, the emphasis in the later stages of the projects was on practical outdoors applications. Full scale applications in collaboration with stakeholder parties involving casting of self-healing concrete irrigation canal elements in Ecuador, patch repair for elimination of leaking cracks of concrete walls using self-healing repair mortar, and reduction of frost damage sensitivity and sealing of cracks in concrete parking decks by application of bacteria-based liquid repair system, proofed the functionality and market potential of these products.