Liquid-fueled reactors exhibit unusual and interesting properties compared to solid-fueled reactors, requesting a revision of some well-known conception and safety rules. Emphasis is thus put in this chapter on such differences and the need for innovative approaches with the focus on homogeneous molten salt reactors. The molten salt fast reactor concept, where the circulating fuel also plays the role of coolant and based on a fast neutron spectrum, is seen as a long-term alternative to solid-fueled fast reactors. It fulfills the Generation-IV criteria and is studied since a decade mainly by calculations and determination of basic physical and chemical properties in European Union and Russian Federation. The main characteristics of this concept are presented and discussed including transient simulation, c