Direct borohydride fuel cells, which convert the chemical energy stored in borohydride directly into electricity, are one of the most promising energy-conversion devices for portable, mobile and Stationary power applications, primarily because they run on a carbon-free fuel and uses the low-cost materials. For this reason, this energy technology has undergone a rapid progress over the last decade. This article provides a comprehensive review of transport phenomena of various species in direct borohydride fuel cells. Particular attention is paid to the understanding of the critical issues related to transportation of various species through the fuel cell structure.