The influence of load and temperature on friction is addressed in a practical way to provide a step forward in simulation-based design through the development and the numerical implementation of realistic system-level models of frictional losses. Hydraulically and electrically supplied actuators are considered at both individual component level (e.g. gear pairs, nut–screws or bearings) and integrated equipment level (e.g. reducers or even complete actuators). The need for more realistic modelling of friction for embedded and more electrical systems is highlighted, and the influence of load and temperature is illustrated from measurements. The state of the art is reviewed considering knowledge models with special focus on physical effects and data commonly supplied by components’ manufacturers. Then, special attention is paid to global representation models developed as a parameterized combination of generic friction effects, and a generic framework for introducing load and temperature effects in system-level friction models is proposed. Candidate options for model structure, parameterization, numerical implementation and inverse simulation are discussed. The last part of this article supports the development of friction models from mechanical efficiency data, the parameter most widely handled by designers and suppliers, with special attention to aiding or opposite load and to sticking. Throughout this article, measured friction forces are extensively reported and compared with the proposed models.