To promote widespread use of fuel cell vehicles (FCVs), further improvement of cold start capability is required for operation in various extreme temperature regions all over the world. Sub-freezing, cold start issues of fuel cells must be resolved through gaining a better understanding of the physical phenomena taking place in a cell during cold start and by elucidating the mechanisms hindering cold startup.Nissan has improved its understanding of the physical phenomena occurring in a fuel cell (FC) during cold startup by a laboratory-scale FC experiment at subfreezing temperatures and a numerical calculation that expresses various transport processes in a fuel cell, including those of the reactant gases, water, electrons and heat. The results have identified several necessary conditions for mass transport in a cell during cold startup and the factors that limit and govern the phenomena involved. For example, the ice formation rate in the cathode catalyst layer, which has a pronounced effect on cold start performance, is substantially influenced by the product water uptake potential and uptake rate of the polymer membrane. It has also been found that the ice formation rate varies significantly depending on the physical properties and initial water content of the membrane, load, temperature and other factors.These findings have been used to improve fuel cell materials and to develop a new 2008 model FC stack that possesses ample cold start capability without having any negative impact on other performance attributes such as durability. Test results obtained with an improved X-TRAIL FCV equipped with this new stack have verified its cold start capability from -20°C and driving performance under subfreezing conditions at the Hokkaido Proving Grounds in Japan.Finally, this paper also touches on some issues that will arise in the future in connection with demands for lower cost FCVs and mentions possible approaches to resolving them.