For around 100 years, the hydrothermal gasification, liquefaction, and carbonization has been studied for conversion of biomass to valuable gas, liquid, and solid products. Influenced by the oil crises, a previous focus has been on the production of fuels by reducing the oxygen content of biomass, therefore also increasing the heating value, and producing gases or oils. In the past mainly "stand-alone" approaches, not e.g. integration in a bio-refinery concept, were investigated. Today, the use of biomass as a carbon resource is the focus, which mean the production of advanced carbon materials by hydrothermal carbonization and of platform chemicals like furfurals. In addition, bio-refinery concepts, with more than one product and those with high added -value are being investigated. Now the question that occurs is, what should the size of a bio-refinery be: the widespread nature of biomass hints to small, decentralized plants while the economy of scale suggests large plants.