Reactive intermediates such as carbocations, carbanions, radicals and radical ions can be electrochemically generated from various electroactive species. Those intermediates may react chemically (C) or electrochemically (E) according to EC, ECE mechanisms. Anodic oxidations produce acidic or electrophilic species, which can react with nucleophiles or (and) eliminate protons or electrophiles. Cathodic reductions afford basic or nucleophilic species, which can react with protons or electrophiles or (and) eliminate nucleophiles. In this way, functional group conversion, substitution reactions, addition reactions, cleavage reactions and coupling reactions can be selectively performed by using direct electrolyses. Activation by transition-metal catalysts is required when the organic substrate is not electroactive or leads to non desired reactions. The metalcatalysed electrosynthesis proceeds by a double activation: i) chemical activation of the organic substrate by the electrogenerated active form of a transition metal catalyst that generates an organometallic species more easily reduced than the organic substrate, ii) followed by activation by electron transfer of the organometallic species formed in the previous chemical activation step. This double chemical and electrochemical activation causes new reactions to proceed, which involve either the classical organic reactive species, produced in any electrochemical steps (carbanions) or organometallic complexes (anionic or neutral) as the basis of new reactivity.