jats:p The notebooks of Leonardo da Vinci (1452–1519) represent a unique source of information on Renaissance technology. They contain numerous references to tribological topics, including designs for bearings based either on rolling elements on axles (disc, cone, and sector bearings) or on freely rolling balls, cones or rollers. This paper provides the first comprehensive study of this material and its context, based on all of Leonardo's surviving manuscripts. While some of his bearing designs (such as the use of sector bearings to support bells) were clearly based on pre-existing technology, he showed a deep understanding of the principles behind them and remarkable ingenuity in developing them further. In some cases, however, these developments suffered from intrinsic defects or were completely impractical for other reasons. Although roller bearings pre-dated the work of Leonardo, the concept of using freely rolling balls in axial bearings appears to have originated with him. </jats:p>