This book presents Computational Fuel Cell Dynamics (CFCD) approaches to analyze the enhanced performance of typical forced convection and self air-breathing PEM fuel cells (ABFC). The mathematical framework used in the simulation is a comprehensive two/three dimensional, multi-component, multiphase, non-isothermal, time-dependent transport computational model, performed using the commercial CFD software (FLUENT 6.3.16) with a PEMFC add-on module and self-developed user subroutines. This work seeks to give a better understanding of design for the enhanced performance of PEMFC (both forced convection and air-breathing fuel cells). This requires the optimal combination of improved reactant mass transport for the electrochemical reaction and keeps the right membrane water content for ionic transfer without causing flooding of the gas diffusion layer.