Organic electrochemistry employs electric current to drive organic synthetic reactions and is attracting renewed interest in the past decade.^3,4 Since electrons do not produce reagent-related waste and are among the cheapest reagents for chemical synthesis, organic electrochemistry holds great promise in developing green and sustainable synthetic methods.⁵ While the majority of the reported organic electrosynthetic reactions rely on direct electrolysis, indirect electrolysis with mediators has been increasingly explored, especially in the past few years.^6–9 The use of mediators not only allows the reactions to proceed under mild electrode potentials to reduce energy consumption and increase selectivity^10,11 but also significantly expands the scope of organic electrosynthesis to many redox inactive compounds through atom transfer catalysis¹² or C–H bond activation.^13–16 In addition, electrolysis with a redox mediator allows the generation of radical intermediates in the bulk solution away from the electrode surface to avoid electrode passivation and reduce their local concentration.⁹ Key to the success of indirect electrosynthesis is the development of mediators that can function under electrochemical conditions. Efforts in the past few years have significantly expanded the list of mediators, some of which are listed in Scheme 1.1A, leading to the rapid development of indirect electrosynthesis. The mediators promote electrochemical reactions through an outer-sphere or inner-sphere mechanism (Scheme 1.1B). In the latter case, a transient adduct is formed between the mediator and substrate either after or before electron transfer on the electrode. In this context, many redox-mediated electrochemical cyclization reactions have been disclosed for the synthesis of various hetero- and carbocycles and will be the focus of this chapter (Scheme 1.1C). These reactions proceed mainly through radical or ionic cyclization to forge the ring structures.