In chemistry, an acetylide is a compound that can be viewed as the result of replacing one or both hydrogen atoms of acetylene (ethyne) HC≡CH by metallic or other cations. Calcium carbide is an important industrial compound, which has long been used to produce acetylene for welding and illumination. It is also a major precursor to vinyl chloride. Other acetylides are reagents in organic synthesis.

The term acetylide is used loosely. It applies to an acetylene RC≡CM, where R = H or a side chain that is usually organic. The nomenclature can be ambiguous with regards to the distinction between compounds of the types MC₂R and M₂C₂. When both hydrogens of acetylene are replaced by metals, the compound can also be called carbide, e.g., calcium carbide Ca²⁺[⁻C≡C⁻], which is calcium acetylide. When only one hydrogen atom is replaced, the anion may be called hydrogen acetylide or the prefix mono- may be attached to the metal, as in monosodium acetylide or sodium hydrogen acetylide, Na⁺[⁻C≡CH]. Metal acetylide may be described as salts, but that description rarely comports with crystallographic analysis.

In the absence of additional ligands, metal acetylides adopt polymeric structures wherein the acetylide groups are bridging ligands. Alkali metal acetylides have the general formula [M₂C₂ (M = Li, Na, K, etc).They are sometimes represented as [M⁺]₂[⁻C≡C⁻] but the C---M bonding might also be described as polar covalent. They dissolve without decomposition in ammonia. Such solutions are proposed to contain solvated ⁻C≡C⁻ ions.

Alkali metal and alkaline earth metal acetylides have the general formula [M'C₂ (M' = Mg, Ca, etc). Rather than salt-like, they can be considered Zintl phase compounds, containing ⁻C≡C⁻ ions, with a triple bond between the two carbon atoms. They undergo ready hydrolysis to form acetylene and metal oxides:

The ⁻C≡C⁻ ion has a closed shell ground state of ¹Σ⁺
_g, making it isoelectronic to a neutral molecule N₂, which may afford it some gas-phase stability. polymeric structures wherein the acetylide groups are bridging ligands.

Acetylides of the transition metals, show evidence of covalent character, e. g. for being neither dissolved nor decomposed by water and by radically different chemical reactions. The inventory of such complexes numbers in the hundreds. Even the stoichiometrically simple silver acetylide and copper acetylide appear highly covalent..

File:XAPGIF2.png | Portion of the structure of the polymer copper(I) phenylacetylide Cu⁺[⁻C≡C−C₆H₅].

Acetylene and terminal alkynes are weak acids: