Summary form only given, as follows. The applications of arcs and plasma torches can be roughly classified in two domains: electrical engineering and thermal (or chemical) processes. In the first category we can consider circuit-breakers, arc lamps and some aspects concerning lightning. In the second category, we can distinguish metallurgical processes (cutting, welding, arc furnaces and metal heating), plasma spraying, particle production and treatment, fullerenes and nanotubes synthesis and waste destruction. In a first part we will present the main properties of arcs and thermal plasmas that explain their use in industrial applications. Then we will show the diagnostic methods and the bases of the modelling developed for analysing the arc behaviour or the processes, and useful for the design and predictions of new apparatus. After this general presentation, we will give some results corresponding to the mutual validation between experiments and models, showing in particular the interest of 3D modelling. Then we will describe more precisely various applications allowing to show the relationship between the technological challenges or problems, and the present main axes of investigation such as instabilities and hydrodynamics problems, interaction with materials and powders, energy (and radiation) transfer and chemical kinetics including the treatment of departures from equilibrium.