This chapter presents an overview of the synthesis of a new class of inorganic additive doped functionalized polymeric membranes or mixed matrix membranes (MMM) and their application in water treatment. Different inorganic additives, with particle sizes ranging from a nanometer to a few micrometers, improve membrane properties such as water flux, hydrophilicity, surface zeta potential and fouling. Morphological characteristics in the micrographic structures of these membranes clearly portray the difference in the performance of pure polymeric and functionalized membranes. The incorporation of functional groups also testifies the uniqueness in behaviour. The alteration in molecular weight cut-off of these membranes due to the impregnation of these particles clearly suggests a change in the pore size of the membrane. It can also be observed that the inorganic additives in the membrane have a selective affinity for ionic contaminants. An increase in surface roughness results in the adherence of the contaminants to the doping material. This behaviour can also be exploited to remove harmful contaminants including fluoride, arsenic, potentially toxic heavy metals such as lead, chromium, copper, etc., selectively. Water treatment by this class of membranes can be cost-effective in comparison to most of the conventional remedial techniques, since removal is maximum at comparatively lower pressure and flow rate, dissipating less energy.