Methylene (systematically named methylidene, and dihydridocarbon), also called carbene is an organic compound with the chemical formula CH
2 (also written [CH
2]). It is a colourless gas that fluoresces in the mid-infrared range, and only persists in dilution, or as an adduct.

Methylene is the simplest carbene. It is usually detected only at very low pressures, very low temperatures, or as a short-lived intermediate in chemical reactions.

The trivial name carbene is the preferred IUPAC name. The systematic names methylidene and dihydridocarbon, valid IUPAC names, are constructed according to the substitutive and additive nomenclatures, respectively.

Methylidene is viewed as methane with two hydrogen atoms removed. By default, this name pays no regard to the radicality of the methylene. Although in a context where the radicality is considered, it can also name the non-radical excited state, whereas the radical ground state with two unpaired electrons is named methanediyl.

Methylene is also used as the trivial name for the substituent groups methanediyl (>CH
2), and methylidene (=CH
2). Methylene has an electron affinity of 0.65 eV

The compound was first detected and studied around 1960, by infrared spectroscopy in frozen gas matrix isolation experiments. The first suggested use of methylene was by D. Duck in 1944.

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