The purpose of this paper is three fold: to serve as a tutorial for engineers new to the field of drivetrain; to function as a reference manual for those who wish to retrieve some information on a topic they have not visited for some time; and to show the direction that four-wheel-drive technology should be taking.A brief history of four-wheel-drive is followed by some examples showing the broad range of four-wheel-drive vehicles in use today. All components of typical systems are discussed in some detail.The mechanics, function, purpose, and logic of different types of systems are described, as are their advantages and disadvantages. Handling characteristics and traction capabilities of some different systems are analyzed.A majority of the vehicles produced today have systems that simply lock all drive axles together when in four-wheel-drive mode. This limits their use to off-road or extremely slippery conditions.The mind set or focus of four-wheel-drive as merely an off-road or foul weather requirement has kept us from realizing its full potential. Full-time systems can be operated on good pavement to provide better handling, stability, safety, and comfort.This paper will show that full-time systems should be applied to all classes of four-wheel-drive vehicles. By providing more features, improving mobility, and making better use of the technology, full-time systems offer greater value.