Carbocations (also called carbenium ions or carbonium ions) are positively charged ions of the general formula R₃C⁺. Like the negatively charged carbanions, they are found as intermediates in a large number of reactions, for example the dissolution of alkenes in strong acids and the dehydrohalogenation of alkyl halides.

Carbocations exhibit a broad range of stability and reactivity. As intermediate compounds they are unstable and rapidly converted to the product of the reaction. These intermediates can only be detected by such techniques as nuclear magnetic resonance. There are several stable compounds that can be formed such as triphenylmethylcarbenium and 1,3,5-cycloheptatriene carbenium (tropylium carbenium). The stability of carbocations increases depending upon whether they have one, two, or three R groups attached to the carbon atom.

Alkyl carbocations can be prepared by reacting the alkyl fluoride and antimony fluoride at low temperature in the presence of sulfur dioxide.

All carbocations are strong alkylating agents with a high affinity for groups which donate or share their electrons (nucleophiles), such as halide ions, hydroxyl anions and amines.

Carbocations are a group of strongly reacting molecules which are rarely encountered in their native form due to their reactivity.