Microbial communities play a vital role in bioelectrochemical systems (BES), enabling sustainable energy generation, wastewater treatment, and bioremediation. These systems utilise the metabolic processes of electroactive microorganisms, facilitating electron transfer between electrodes and substrates. The diversity, composition, and interactions of microbial consortia have a significant impact on the efficiency and performance of biogas energy systems (BES). Key groups, such as Geobacter, Shewanella, and Pseudomonas, are recognised for their ability to conduct extracellular electron transfer (EET), which contributes to power generation and pollutant degradation. The microbial community structures in BES are shaped by environmental factors, electrode materials, and operational parameters, which in turn affect biofilm formation and electron transfer pathways. Understanding these complex microbial interactions is essential for optimising BES performance and stability. Advances in omics technologies, including metagenomics, transcriptomics, and proteomics, have provided more profound insights into microbial dynamics and functional roles in BES. Future research aims to engineer microbial communities through synthetic biology and adaptive evolution to elevate electron transfer efficiency and system robustness. This review examines the current understanding of microbial communities in Bioelectrochemical systems, their functional mechanisms, and strategies to enhance their application in energy and environmental sustainability. A comprehensive understanding of these microbial interactions will drive the development of more efficient and scalable bioreactor systems (BES) technologies.