Polymer-nanoparticle composite materials have unique characteristics, such as high mechanical strength, good electrical conductivity, optical and thermal properties. Nanoparticles can gain high functionality and therefore they increase the overall performance of conventional materials, such as membranes, used in environmental applications. Membrane separation properties can be controlled for each specific application by the proper choice of fabrication components (main polymer, solvent, additives like nanoparticles, pore forming agents, etc.) and parameters (evaporation time and temperature, coagulation bath temperature, etc.). Moreover, especially in recent years, the membrane fouling problem can be avoided with different membrane fabrication components. Membrane fouling can be defined as the uncontrolled deposition of particles, colloids, macromolecules or salt ions from feed solution at the membrane surface or inside the membrane pores. It is a severe problem for membrane materials used in pressure-driven processes such as reverse osmosis (RO), nanofiltration (NF), ultrafiltration (UF), and microfiltration (MF) and also for other membrane processes. Different polymers (Polyethersulfone (PES), polysulfone (PS), cellulose acetate (CA), polyvinylidene fluoride (PVDF), etc.) could be selected as membrane materials for these membrane systems according to their physical and chemical characteristics, such as good chemical, heat, mechanical and cleaning resistance and environmental endurance, as well as easy processing and manufacturing. For instance, the intrinsic hydrophobicities of some polymers are high and so this results in hydrophobic membrane materials and leads to a low membrane flux, poor anti-fouling properties and low application and useful life. The fouling causes a decrease in membrane performance, either temporarily or permanently. The fouling mechanism includes the interaction between the membrane surface and the foulants (inorganic, organic, and biological substances in many different forms). The foulant molecules not only physically interact with the membrane surface but also chemically degrade the membrane material. Most of the latest membrane fouling studies focused on the physical or chemical modification of membrane material for low fouling properties. These studies can be summarized in three main areas; (i) the modification of the membrane surface with in-situ physical and chemical treatments, (ii) the coating of the membrane with special materials that have low fouling properties and (iii) the preparation of the membrane by adding nanomaterials (mixed matrix membranes, MMMs). MMMs are formed by the addition of inorganic or metal oxide particles, having micrometer or nanometer sizes, to the polymeric casting solution or by in-situ generation. Over the past few years, the rapid growth in nanotechnology has aroused significant interest in the use of nanomaterials in membrane applications. So far, the membrane modification studies using nanotechnological methods in particular have achieved useful results. Nanoparticles (NPs) are defined as particles having the size of 1–100 nm and they have unique magnetic, electrical, optical, mechanical and structural properties. More recently, several natural and engineered nanomaterials have also proved to have exceptional properties, including chitosan, silver nanoparticles (nAg), photocatalytic TiO2, fullerol, aqueous fullerene nanoparticles (nC60), and carbon nanotubes (CNT). Moreover, some nanoparticles, such as silver (Ag), copper (Cu), zinc oxide (ZnO), titanium oxide (TiO2), etc., have antibacterial properties and thus show high toxicity to a broad spectrum of microorganisms, including bacteria, fungi, viruses and yeasts, and have been studied as antibacterial agents in different areas. The combination of membrane chemistry and the antibacterial properties of NPs may particularly solve the biofouling problem in membrane systems. To prevent fouling problems, NPs can be applied by directly coating on to the membrane surface or by blending in the polymer matrix of the membrane during the membrane fabrication process.