The integration of microbial electrolysis cells (MECs) into anaerobic digestion (AD) systems presents a pioneering avenue in sustainable waste treatment and renewable energy production. Anaerobic digestion is a promising technology for concurrent waste treatment and bioenergy production; however, the bottlenecks include long start-up times, low methane content, and sensitivity toward environmental change. One of the standout features of MECs integrated in AD is the ability to limit start-up time by generating micro-aerobic conditions which enhance the rate of hydrolysis and thereby reduce start-up times. Besides decreasing the start-up time, micro-aerobic conditions improve the removal of organic matter by increasing the hydrolysis rate. Moreover, MECs generate hydrogen, enhancing both the combustibility of biogas and its methane content through hydrogenotrophic methanogenesis. Furthermore, the poor performance of anaerobic digestion at low temperatures can be potentially improved by promoting hydrogenotrophic methanogenesis as an alternative to the rate-limiting acetoclastic methanogenesis. Additionally, MECs offer a solution to a common challenge in anaerobic digestion systems—inhibitory compounds. MECs can mitigate inhibitory effects by electrochemically removing them. This not only aids in waste treatment but also opens doors for the digestion of a wider range of feedstocks. Nevertheless, as with emerging technologies, challenges persist. These encompass the optimization of MEC design and operation, material durability improvement, and overall cost-effectiveness enhancement. As research progresses, surmounting these hurdles is pivotal for the widespread adoption of MECs in AD systems. This chapter provides an overview of the state-of-the-art development of AD-MEC systems, emphasizing their potential to alleviate bottlenecks, optimize design and operation, enhance material resilience, and improve cost-effectiveness, unlocking the technology’s vast potential across various industries.