Nowadays, the implementation of nanotechnology in various industry sectors is widely recognized and accepted as a promising tool due to its significant advantages. There are various types of material nanocomposites based on their main applications. Many classes of nanocomposites include polymers as matrix components or as fillers/reinforcements. These classes are collectively referred to as polymer nanocomposites. In addition to nanocomposites, micro- and macro-composites have been established as essential polymeric materials due to their wide applications over the decades. The book chapter outlines the major differences between nano-, micro-, and macro-composites regarding the internal structuring and sizes of their constitutive components, focusing on their main properties, applications, and recyclability. In terms of polymer composite applications and targeted properties, these materials can be viewed as polymers impregnated with inorganic or organic compounds. Essentially, the added inorganic or organic compound serves as a reinforcement or filler, enhancing the mechanical and thermal properties. However, nanotechnology extends the role of the added component to impart new specific properties such as barrier characteristics, antifouling, antimicrobial effects, conductivity, and more. The structure and composition of polymer composites influence the recycling management, guiding it toward appropriate procedures. Generally, the recycling process for composites is more complex compared to single polymeric materials, as separating the components of recyclable composites is more intricate, costly, and less economical. Because of this, many industrial polymeric composites are termed hard-to-recycle composites. Despite these challenges, manufacturers are driven to use and produce polymeric composites effectively due to their significant advantages. The book chapter recapitulates the major types of polymer matrices and possible polymer additives for the development and production of polymer composites. Therefore, the classification of polymers considers the polymer source: fully extracted from biomass (natural), biosynthesized via microbial fermentation, monomers extracted from biomass, natural polymers modified by synthetic procedures, and synthetic polymers derived from fuel sources. Furthermore, the book chapter addresses the inorganic and organic additives that form polymer composites. This approach is very important as it highlights the sustainability, reliability, and environmental friendliness of each type of polymer or additive, including rubbers, fibers, thermosets, bioplastics, bio-based, non-bio-based, biodegradable, and non-biodegradable materials. Each polymer class is presented in the context of its specific recyclable pathway and the complexity of recycling as a composite versus simple polymers, focusing on aspects such as separation and recovery. The general and newly developed recycling pathways are highlighted according to polymer and additive categories (from primary to quaternary/energy recovery): mechanical recycling, chemical recycling (partial or total monomer reconversion), pyrolysis, thermal treatment, enzyme-catalyzed processes, microbial degradation, and more. The final section provides valuable information on the importance of composite recycling and its contribution to the circular economy.