Membranes are used in desalination or water treatment to separate pollutants from water based on characteristics such as size or charge. Nanofiltration (NF), ultrafiltration (UF), microfiltration (MF), and reverse osmosis (RO) are typical membrane techniques. However, traditional membranes have a number of disadvantages, including fouling both on surfaces and in internal structure, uncontrollable pore size, and membrane features. Smart membranes, also known as stimuli-responsive membranes, have recently attracted attention due to their selectivity, tunable permeability, and tunable and/or reversible attributes. This new generation of smart membranes is created by integrating various stimuli-responsive materials into membrane substrates. These multi-functional smart membranes can self-adjust their physical and chemical features in response to environmental signals such as temperature, pH, light, and other stimuli. Thermo-responsive membranes, pH-responsive membranes, ion-responsive membranes, molecule-responsive membranes, UV-light-responsive membranes, glucose-responsive membranes, magnetic-responsive membranes, and redox-responsive membranes are the current kinds of smart membranes. Because of their smart structures, they have the potential to improve performance by providing high selectivity without reducing permeability, high mechanical stability, and high resistance against fouling, and can meet requirements such as molecular weight cut-off (MWCO), removal efficiencies, and wastewater quality. Smart membranes can show tuneable features based on the condition of the stimulus or stimuli present internally or externally, resulting in improved and desirable controllability over the process of pollutant removal from water. Because of their physicochemical stability, repeatability, and long life, stimuli-responsive smart materials (mainly adsorbents and filtration membranes) have the potential to be key materials for membrane production, particularly in the field of water treatment. Smart membranes have a bright future, and it is important to investigate and encourage their use and advancement. This review provides a comprehensive overview of smart membranes.