Alkyne metathesis is a catalytic redistribution of carbon–carbon triple bonds in which two alkynes exchange alkylidyne fragments, formally 2 R1C≡CR2 ⇌ R1C≡CR1 + R2C≡CR2, through a metallacyclobutadiene intermediate. Modern alkyne-metathesis methods use high-oxidation-state molybdenum or tungsten alkylidyne complexes ^[1]. The exchange proceeds through metallacyclobutadiene formation and establishes an equilibrium among alkyne constituents ^[2]. Silyloxy-supported molybdenum alkylidynes exemplify well-defined catalysts whose activity and functional-group tolerance are governed by the ancillary ligand set ^[3]. The process is the triple-bond analogue of alkene metathesis: the elementary cleavage and recombination involve C≡C rather than C=C units, and the resting catalytic species is an alkylidyne rather than an alkylidene. Ring-closing, ring-opening, and acyclic cross-metathesis of alkynes are the same transformation under different connectivity constraints. The concept excludes alkyne polymerization by repeated insertion and excludes enyne metathesis, which mixes alkene and alkyne partners. Product distribution is equilibrium-controlled unless a volatile alkyne is removed or a ring strain bias is imposed.