For the obtained materials, the Italian researchers observed good matrix/fiber adhesion and mechanical behavior in terms of break stress and composite stiffness [9]. [PERSON] and colleagues, by mixing ferromagnetic nickel micro-powders with polyurethane (PU) shape memory polymer (SMP)/dimethylformamide solution, prepared a micron-sized protrusive PU SMP composite, curing the mixture under a low magnetic field [10]. Morphology and thermal tests were carried out by the authors to show the hybrid composites' potential applications for micro-electro-mechanical systems (MEMS) and biomedical devices. Polydimethylsiloxane (PDMS)-based composites were fabricated by [PERSON] et al. to study their optical transmittance properties. With a simple production process, the Chinese researchers checked the materials' transmittance by varying the microcrystalline graphite powder concentration or the composite film's thickness, thus obtaining a wide range of transmittance properties [11]. [PERSON] and coworkers designed a new hybrid catalyst based on activated carbon (AC)-supported sulfonated cobalt phthalocyanine (AC-CoPCS) [12]. Firstly, they spectroscopically investigated the prepared catalyst to characterize its structure and then its catalytic performance, finding superior behavior in terms of yield and purity with good industrial application prospects. The first of the three reviews in this Special Issue is by [PERSON] and colleagues, who present the most outstanding advances in the rheological performance of magneto-rheological elastomer (MRE) composites. They focus on filler distribution, arrangement and wettability within elastomer matrices, and their contribution towards the performance of the mechanical response when subjected to a magnetic field are evaluated. Particular attention is devoted to the understanding of their internal micro-structures, filler-filler adhesion, filler-matrix adhesion and the viscoelastic behavior of the MRE composite under static (valve), compressive (squeeze) and dynamic (shear) modes [13]. A short review, on the effect of surfactants on the mechanico-thermal properties of polymer nanocomposites, was then proposed by [PERSON] and [PERSON] [14], highlighting polymer nanocomposites as a function of the surfactants used in their modification, namely surfactant-modified inorganic nanofiller/polymer nanocomposites and surfactant-modified organic nanofiller/polymer nanocomposites. The effect of surfactants on their mechanical and thermal properties is also shortly reviewed, with an attempt to capture the interest of the polymer composite researchers and encourage the further enhancement of new theories in this research field. Finally, [PERSON] et al., focus their attention on the progress in hybrid solar cells based on solution-processed organic and semiconductor nanocrystals, analyzing perspectives on the device design [15]. They give a brief introduction to the progress on solution-processed organic/inorganic semiconductor hybrid solar cells, including a summary of the development of hybrid solar cells in recent years, the strategy of creating hybrid solar cells with different structures and the incorporation of new organic hole transport materials, with new insights into device processing for high efficiency. The author declares no conflict of interest.