A fuel cell clearly is a multidisciplinary system. The authors have chosen an original energy approach that they have applied via the Bond Graph formalism. A PEM fuel cell Bond Graph model is proposed and detailed. Its potentialities are then illustrated by studies on the fuel cell dynamic behavior (current harmonic effects, etc.) and system simulations (electricity generating unit based on a PEM fuel cell, etc.). (c) 2005 Published by Elsevier B.V.