碳－碳键是一连接两个碳原子的共价键。其中最普通的形式是单键：即一个键是由两个电子组成，其中两个原子分别提供一个电子。碳－碳单键属于σ键,组成单键的两个碳原子自身的电子先形成混成轨域，然后两个混成轨域之间形成碳－碳单键，例如乙烷的两个碳原子就是形成sp混成轨域，但碳的单键也有形成其他混成轨域的例子（例如sp对sp）。其实单键二端的的碳原子不一定要形成相同的混成轨域。在烯烃中碳原子会形成双键，在炔烃中碳原子会形成三键。双键的组成是一个σ键（由两个形成sp混成轨域的电子）和一个π键（由两个未参与混成的p轨域电子所构成)。三键则是一个sp混成轨域和二个p轨域所构成，其中二个原子各提供一个p轨域。双键及三键中使用的p轨域会形成π键。当碳-碳键数愈多，键能愈大，键长愈短。

A carbon–carbon bond is a covalent bond between two carbon atoms. The most common form is the single bond: a bond composed of two electrons, one from each of the two atoms. The carbon–carbon single bond is a sigma bond and is formed between one hybridized orbital from each of the carbon atoms. In ethane, the orbitals are sp hybridized orbitals, but single bonds formed between carbon atoms with other hybridisations do occur (e.g. sp to sp). In fact, the carbon atoms in the single bond need not be of the same hybridisation. Carbon atoms can also form double bonds in compounds called alkenes or triple bonds in compounds called alkynes. A double bond is formed with an sp hybridized orbital and a p-orbital that isn't involved in the hybridization. A triple bond is formed with an sp hybridized orbital and two p-orbitals from each atom. The use of the p-orbitals forms a pi bond.