The efficiency of microbial fuel cells (MFCs) is affected by several factors such as activation overpotentials, ohmic losses and concentration polarization. These factors are handled in micro-sized MFCs using special electrodes with physically or chemically modified surfaces constructed with specified materials. Most of the existing mu Lscale MFCs show great potential in rapid screening of electrochemically-active microbes and electrode performance; although they generate significantly lower volumetric power density compared with their mL counterparts because of their high internal resistance. This review presents the development of microfluidic MFCs, with summarization of their advantages and challenges, and focuses on the efforts done to minimize the adverse effects of internal resistance (ohmic and non-ohmic) on their performance. (C) 2013 Elsevier Ltd. All rights reserved.