Publisher Summary This chapter discusses metal–isocyanide chemistry. In the interim, reviews have appeared on specific aspects of isocyanide chemistry. The generally accepted valence bond and molecular orbital (MO) approach to the bonding of metal isocyanides has been well described in Treichel's review, and has been used to rationalize variations in infrared (IR) stretching frequencies between bonded and nonbonded isocyanides and the better π-acceptor qualities of aryl versus alkyl isocyanide groups. A number of new synthetic routes to isocyanide complexes of chromium, molybdenum, and tungsten have been investigated. A number of attempts have been made over the years to develop reproducible synthetic routes to six- and seven-coordinate isocyanide complexes of molybdenum and tungsten. A number of routes have been employed for the synthesis of metal–isocyanide complexes by generating the isocyanide ligand on the metal atom. A number of monomeric complexes have been prepared, which may be considered as substitution products of the [Co(CNR)5]+ and [M(CNR)4]+ cations. Electrochemical investigations have been reported on a range of homoleptic and mixed carbonyl–isocyanide complexes, in attempts to rationalize substituent effects on the isocyanide with the electronic structure of the metal. Insertion reactions of isonitriles into metal–alkyl or metal–aryl bonds are now well established, occurring with metal–alkyl or –aryl groups from group IVA to IB and, recently, with uranium and thorium carbon bonds.