The possibility of application of the biomass as source of thermal energy is known and effected within an extended scope. The co-combustion of coal and biomass is however a not completely recognised process. Taking into account the differences of particular types of furnaces there are different conditions of combustion and requirements for fuels. In general the direct replacement of coal fuels with alternative fuels (including biomass) leads to decrease of efficiency of power industry plants. Suitable quantitative and qualitative selection of biomass for co-combustion with coal brings several positive ecological and economic results. On one hand one can utilise reasonably the wastes of biomass and/or utilise the barren lands and degraded areas for the acquirement of biomass, on the other hand the production of thermal energy involving the biomass decreases the emission of pollution to environment and can bring additional profits. The permanent implementation of the co-combustion of coal with biomass requires the solution of several organisational, technological and technical problems and in particular the economic ones.