The aim of this chapter is to review the technology that might be found within the drivetrain of a vehicle and make the link to the lubricants used within those units. The lubricant is arguably the most important single component within the drivetrain, although it is often the most difficult to improve, modify, or develop. However, in investigating the drivetrain of the vehicle, some boundaries need placing around the problem. Before starting, it is also worth pointing out that the reader may well come across or be familiar with the term “driveline”. It is probably reasonable to say that “drivetrain” and “driveline” are terms that are interchangeable, although some engineers may have some subtle distinction between the two.