Ceramic fuels used for fast reactors (FRs) are oxide fuels and nonoxide ceramic (MX-type, where M stands for U and Pu and X stands for C and N) fuels such as carbide and nitride fuels. Ceramic fuel-cladding interactions (FCCI, fuel and cladding chemical interaction) are mainly divided according to oxide and MX-type fuels. FCCI is more complicated in oxide fuels than in MX-type fuels because oxide fuels lead to oxidation of cladding materials and formation of various oxides of fission products (FPs) by irradiation. Unlike the case of oxide fuels, FPs from MX-type fuels do not play a major role in FCCI. Instead, the carburizing and nitriding of cladding, and also the formation of intermetallic compounds of fuel and cladding, have been investigated as a major FCCI of MX-type fuels.FCCI is nowadays recognized as one of the major factors determining integrity and lifetime of oxide fuel pins as demonstrated in numerous in-pile and out-of-pile tests. Some mechanisms of cladding attack have been proposed from the results of the many postirradiation investigations and thermodynamic analyses of the postulated chemical reactions. At present, it is clear that the knowledge base for MX-type fuels is much smaller and less detailed than that for oxide fuels, and addition to the base is a work in progress. However, MX-type fuels merit much less concern regarding cladding-fuel compatibility than oxide fuels.In this chapter, the causes of FCCI with oxide fuels are reviewed, considering the dependence on irradiation conditions and fuel parameters as well as the types of cladding material. Furthermore, the role of corrosive FPs in the FCCI, the mechanism of FCCI, and the FCCI enhancement by oxygen potential are summarized. The MX-type fuel-cladding interaction is also briefly reviewed. © 2012 Elsevier Ltd All rights reserved.