Nanoparticles (NPs) of different types, especially those of metals and metal oxides, are widely used in research and industry for a variety of applications utilizing their unique physical and chemical properties. Polymers as plastic, flexible, easily processed and formed materials are attractive supporting and hosting media for NPs. In this chapter, recent research results on formation of polymer composites with NPs produced by means of gas-aggregation (cluster beam technique) are presented focusing on advantages of this method compared to other synthesis routes and showing a number of examples on different approaches providing deposition and implantation of clusters into polymer films, namely: soft-landing of NPs followed by thermal annealing to embed the NPs in a controllable manner; use of supersonic beams with sufficient kinetic energy for the implantation of clusters into thin layers and sequential or codeposition of the clusters and plasma polymers. These ways allow producing of composites with well-controlled and required characteristics. Second part of the chapter overviews applications of polymer composites with metal and metal-oxide NPs as functional materials and devices emphasizing the research on elastomeric electrodes, paper electronic components, memristors for neuromorphic architectures, plasmonic media with tunable parameters, transducers for gas and biosensors, coatings for precise control of wettability or surface interaction with biomolecules or cells, antibacterial media, etc. The review is finalized by outlook on future perspectives of the cluster beam technique in application to polymer materials and conclusions.