Membrane-based separation processes utilize semi-permeable membranes to remove solids, pathogens, and contaminants from water. Deployment of these technologies can help to sustainably increase the supply of potable, agricultural, and industrial water. Despite considerable development in the last decades, several design obstacles still hamper the progress of these systems. For example, membrane fouling is the process during which a contaminant layer forms at the membrane surface, resulting in a loss of productivity and membrane life. While fouling is virtually unavoidable, its reduction would improve the efficiency of membrane technologies significantly. Process optimization and the development of novel ways to deploy and operate the membranes will also contribute to improve water and wastewater treatment. This presentation will review some recent work aimed at the advancement of polymeric membranes and at the optimization of the overall treatment systems. In particular, it will focus on our experiences in reverse osmosis and forward osmosis processes. We will also highlight how chemistry, materials science, and engineering need to necessarily progress hand in hand to achieve breakthrough and consequential results in this field.