The recycling of plastics from homogeneous waste is already state of the art and is also gaining importance for mixed solid waste due to increasing legal pressure. It is known that mixed commercial waste as well as mixed municipal waste contain relevant amounts of plastics. These wastes are usually treated in waste incineration plants or processed into solid recovered fuel for co-incineration. In order to achieve future recycling targets, diverting plastics from these wastes from thermal recovery to mechanical or chemical recycling is a promising option. This doctoral thesis therefore considers different aspects of a possible value creation of plastics from mixed, solid wastes along their value chain from waste to plastics processing. In order to assess the potential of different types of plastics from mixed waste streams for recycling, their content was determined depending on their object dimension (2D and 3D) in pre-shredded mixed commercial and municipal waste at particle size level. It was found that both wastes have a relevant plastic potential (>15%) in different particle size classes and dimensions. As a result, in trials on the mechanical pre-processing of these wastes to produce plastics-rich fractions, it was found that pre-screening by means of a drum screen leads to an increase in the efficiency of the downstream units (e.g. separation performance of a ballistic separator). However, the separation performance of a subsequent, sensor-based sorting aggregate is negatively influenced by the short-, medium- and long-term mass and volume flow fluctuations generated. Further investigations have shown that the two-dimensional, plastic-rich output fractions produced have high polyolefin contents (>50%), which can be recovered using wet-mechanical density separation processes with simultaneous particle cleaning. The investigated dry-processing followed by wet-processing thus appears to be suitable for recovering certain plastics from mixed solid waste for subsequent recycling. The generated plastic streams (mixed/sorted, washed/unwashed) were investigated in terms of their basic processability and achievable thermal, mechanical and rheological material properties. It was found that the materials are processable by compression moulding, homogenisable by compounding and acceptable material properties are achieved. Finally, a benchmark study analysing the relationship between market prices and qualities of plastic flakes and recyclates is cited in this thesis. The steering of plastics from mixed, solid commercial and municipal waste for thermal recovery into recycling is thus technically feasible and would make an important contribution to the achievement of recycling targets, resource conservation and greenhouse gas and waste reduction.