Book excerpt: Focusing on preparation and applications in synthesis and catalysis, this book finally closes a gap in the literature by summarizing this hot topic for the first time. As such, it gathers in one volume the key features of metal vinylidene and allenylidene complexes as well as reactive species and covers applications in metathesis, polymerization, molecular materials, carbon rich compounds and fine chemical production. The emphasis here is on the selective transformations of alkynes and enynes plus simple and complex molecules containing a triple C-C bond. The result is a must-have ready reference for organic, catalytic, complex, theoretical and polymer chemists, as well as those working with/on organometallics.