Worldwide manufacturing, as well as the transportation industry, is greatly affected by the rising costs of energy, maintenance, replacement of expensive and crucial components, and environmental legislations. Diverse solutions have been proposed to meet these challenges: more efficient processes that minimize energy consumption, weight reductions, as well as achieving longer maintenance periods and longer replacement times for tooling and components. In order to find a solution for these issues, nanoparticles (NPs) have been used as additives in conventional lubricants decreasing the coefficient of friction (COF) and wear of elements working under relative motion and loading. Due to environmental and health concerns, recent studies have focused on utilizing eco-friendly NPs, minimizing the usage of hazardous materials and additives. These NPs have demonstrated to be highly efficient increasing wear resistance and lowering COF through several tribological mechanisms. Furthermore, ecofriendly NPs may also help reduce energy consumption in manufacturing processes, hence reducing carbon footprint. This chapter provides the state of the art of eco-friendly NPs for improving tribological properties in conventional lubricants, their tribological testing and evaluation methods, and tribological mechanisms.