The goal of the PAC-Car project, a joint undertaking of ETH Zurich and its partners, was to build a vehicle powered by a hydrogen fuel cell system that uses as little fuel as possible. PAC-Car II set a new world record in fuel efficient driving (the equivalent of 5,385 km per liter of gasoline) during the Shell Eco-marathon in Ladoux (France) on June 26, 2005.This book, addressed to graduate students, engineering professors and others interested in fuel economy contests, is the first to summarize the issues involved when designing and constructing a vehicle for fuel economy competitions. It describes the adventure of developing the PAC-Car II and others some specific technical advice for anyone who wants to design an ultra-lightweight land vehicle, whatever its energy source.