Mild Combustion processes evolve in a temperature and concentration range outside the limit of interest of standard combustion processes, with the aim of lowering the maximum temperature of the whole process below the value at which massive pollutants formation occurs. It represents a trade-off for the optimization of fuel conversion with respect to efficiency (energy saving and pollutant abatement) while keeping configurations of traditional processes. Stability, nearly homogeneous temperature and concentration profiles, reduction and abatement of pollutants as well as very specific oxidative structures, different from the traditional thin flame, makes Mild Combustion a unique process, in terms of environmental sustainability. Starting from the rigorous definition of Mild Combustion, in this chapter an overview of the main features of this process is given, underlining the gaps of basic knowledge that have to be filled with the aim of optimizing the process in relation to specific applications. It is followed by the classification of possible Mild Combustion in different configurations on the basis of the acquired categories both in fundamental and in traditional combustion processes. Although the basic comprehension on Mild Combustion lacks of several aspects, the empirical knowledge of the process is enough to make several industrial facility working in these operative conditions. Thus, the main characteristics of such applications are described with particular regard to energy conversion, material treatment and pollutant abatement plants.