Microbial electrolysis cells (MECs) are bioelectrochemical reactors in which chemical energy stored in organic compounds are converted to hydrogen through biocatalytic oxidation by microorganisms. The performance of MECs is highly affected by microbial communities that are impartible parts of this technology. A better understanding of microbial interactions and competitions mechanisms, has aided the comprehension of ideas and guidelines for cost effective commercial scales design. In this study, a comprehensive review of current knowledge in the microbial characterization, enrichment, and evaluation of effective parameters of microbial community in microbial electrolysis cells for typical biohydrogen production is summarized. Some existing challenges of biocatalysts behaviors in MECs (such as undesirable microorganisms growth and deactivation of desirable species) were disclosed, and outlooks for future research were also proposed, which would aid the acquisition of knowledge and contribute to the development of MECs and their application in bioenergy production with simultaneous treatment of wastewater. Copyright (c) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.