In the last century, polymers have dominated the materials market, and in the later part of the 20 th century, the possibility to further improve their properties and expand their applications was explored by combining polymers with reinforcing elements. This practice has become common, enabling the definition of the composites as the reference materials of the 21 st century and, thus, their occupying of an important portion of the market in the production of modern plastics [1]. The composites are designed by adding a second component to the matrix (generally polymeric) to enhance their properties and/or to achieve specific functions [2]. Among the various composites, the organic-inorganic hybrid materials offer much better performance than their non-hybrid counterparts [3]. The dramatic improvement in physical properties achieved with the incorporation of inorganic particles or nanoparticles into an organic polymeric matrix could bridge the gap between ceramics and polymers. This Special Issue, which consists of 12 articles, including three review articles, written by research groups of experts in the field, considers recent research on polymeric composite materials. Since increasing attention is, today, devoted to composite materials with low flammability, [PERSON] and coworkers used the layer-by-layer (LDL) technique to form multilayered protective coatings for polyamide 6/montmorillonite (PA6/MMT) hybrid nanocomposites [4]. Their results confirmed the success in applying the LDL technique to improve the flammability characteristics of the composites under investigation, reducing the maximum point of heat release rate (PHRR). [PERSON] et al. investigated the interfacial adhesion of a Ni-Ti shape memory alloy with Poly (methyl methacrylate) (PMMA) as the matrix. They studied, by the means of thermomechanical analysis (TMA) and dynamic mechanical analysis (DMA), the surface pattern of the Ni-Ti channeled by a solid-state laser machine. The PMMA matrix, so modified, showed an increase in adhesion of about 80% in comparison to the free plain surface, showing, in the meantime, a reduction in the shape-memory properties of the composite material [5]. [PERSON] and his working group, considering that the traditional fabrication methods of 3D scaffolds and cell-laden hydrogels still face many difficulties and challenges, proposed a new 3D fabrication technique exiting the concept of recycling the unutilized resource [6]. They prepared an innovative fish gelatin (FG) methacrylate polymer hydrogel mixed with a strontium-doped calcium silicate powder (FGSr) 3D scaffold via photo-crosslinking. Their mechanical assessment indicated an increase in the tensile strength of FGSr, thus making it a better candidate for future clinical applications. Furthermore, they observed good biocompatibility with human Wharton jelly-derived mesenchymal stem cells (WJMSC), as well as the enhancement of the osteogenic differentiation of WJMSC. [PERSON] et al. have engaged in the challenge of preparing compact engineering composites with a combination of citric acid and glycerol. Polycondensation-type thermoset resins from natural reactants, such as citric and glutaratic acid, as well as 1,3-propanediol and glycerol, were prepared and analyzed by thermogravimetric analysis (TGA), not only showing that shredded poultry feathers increased the conversion and the reaction rate of the citric acid/glycerol combination but also that increasing the amount of feathers continuously decreased the number of visible bubbles [7]. [PERSON] et al., by using the sol-gel method, prepared silica-based hybrid organic/inorganic amorphous composites with polycaprolactone [8]. They spectroscopically characterized the obtained composites and assessed their bioactivity and antimicrobial behavior, aiming at proposing them for bone implants. Poly(lactic acid) (PLA)-based biocomposites reinforced with flax fibers were designed and prepared by [PERSON] and coworkers by melt blending and a co-rotating conical twin-screw extruder.