The most ubiquitous method for the recycling of solid plastic waste is mechanical recycling, in which the plastic is collected, sorted, washed and grinded into small flakes. This regrind can be used as secondary raw material, either ‘as is’ or after re-extrusion into pellets. For post-industrial waste, such methods can be quite straightforward, as the waste is often composed of a single (well-known) polymer and little to no pollution occurs. Post-consumer waste, however, is far more complex in nature. The materials are often polluted by organic waste or contaminated with non-polymer materials, multiple polymers are usually collected in one batch and there is a variation in all of this between batches. These factors make it nigh impossible to identify the exact composition of post-consumer secondary plastic materials and have an additional negative effect on the polymer quality, on top of the thermomechanical degradation which will occur with every reprocessing step of thermoplastics. For example, it is a well-known phenomenon that different polymers do not mix in the melt phase, even if they are as similar to one another as poly-ethylene and polypropylene. This phase segregation during processing will lead to reduced mechanical properties, toughness foremost among them. This lecture will give an overview of the current state-of-the-art in mechanical recycling of post-consumer solid plastic waste, discuss the remaining scientific challenges in the field and highlight how academic research can support the industry in improving both the quality and quantity of this secondary material source.