Electrocoagulation (EC) has emerged as a viable approach for the treatment of wastewater contaminated with various pollutants. The process has been shown to be suitable for a wide range of applications, including the pollutants of emerging concern such as a nanoparticle, microplastics, endocrine disrupters, oil and grease, pesticides, and pharmaceuticals. Numerous studies have been carried out to improve the performance of the EC process by developing the design of EC reactors. Reactor designs for electrocoagulation can vary based on factors such as the treatment scale, reactor shape, operating conditions (electrode arrangement and configuration, current density, energy sources), operating mode (batch or continuous), and removal efficiency. Therefore, various reactor configurations have been developed and optimized, including batch reactors, continuous flow reactors, packed bed reactors, membrane reactors, and hybrid systems. Each design has distinct advantages and disadvantages that affect aspects such as treatment efficiency, scalability, and operating costs. This chapter presents and explains the basic concepts of electrocoagulation, examines the important parameters affecting reactor design, and assesses the performance of various reactor designs documented in the literature. It also highlights the potential for innovative approaches to address critical environmental issues and promote sustainable water management practices.