Friction modifiers are added to lubricants in order to reduce friction and wear in machine components. They are particularly important in the boundary lubrication regime, where they can prevent solid surfaces from coming into direct contact, substantially reducing friction and wear. Several classes of friction modifier additives exist, the main examples being organic friction modifiers (OFMs), oil-soluble organo-molybdenum additives, functionalized polymers, and dispersed nanoparticles. Reduction of frictional losses and through more efficient lubrication is a key target in order to reduce carbon dioxide emissions. One approach has been to progressively reduce lubricant viscosity to minimize hydrodynamic shear, churning and pumping losses. However, this means that an increased number of components operate under boundary lubrication conditions. This has led to a resurgence in interest in friction modifier additives, particularly OFMs. For example, recent tribology experiments and molecular dynamics simulations have given new insights into their behaviour under boundary lubrication conditions.