Tool use is a remarkable aspect of human hand function. It is suggested that we used tools ‘as if they were part of our body’. Normal hand movements are efficient partly because they rely on internal models, allowing the brain to predict the sensorimotor consequences of motor commands. Tools alter that relationship between hand movements and their consequences, so this anticipatory control requires the brain to also model the properties of the tool. This thesis aims to examine if the visuomotor system can account for the alteration between hand opening and tool opening when planning and executing movements, and if it does so by developing internal models of tools. This thesis also aims to examine the process of acquisition of those internal models of tools. Using grasping as a main task, our first study examined the learning of pliers-like tools with different ratios of tool opening to hand opening. We probed the learning of the tool models by measuring movement kinematics with motion capture. We found limited evidence that people develop internal tool-models, equivalent to those of the hand. People do compensate for the effects of the tool, but some tool geometry were more difficult to learn than others. Our second study examined whether the visuomotor system learns distinct tool mappings, or whether tool properties are accounted for by adapting the hand representation. The study also examine whether tool geometry was accounted for in perceptual tasks. Our results indicated that adaptation was not the principal mechanism behind the accounting of tool properties and that tool geometry was not accounted for during perceptual tasks. Our last study dissociated the contribution of tool complexity and the requirement to make unusual hand movements, to confirm that tool geometry per se contributes to difficulty learning a novel tool. We used a tool that does not behave qualitatively like the hand. Our results indicated that both factors play a significant role. Overall, our results are not consistent with the idea that tools are ‘used as body parts’, but instead with a visually controlled strategy.