Constructed wetlands are proven to be cost-effective, reliable, and alternative technology in treating wastewater because the implementation of conventional wastewater treatment methods in developing countries has higher operation and maintenance costs. It also reduces the disposal of waste into natural wetlands and helps in maintaining biodiversity. Constructed wetlands are called man-made wetlands and can be used for treating municipal wastewater, agricultural runoff, and mine drainage. Through this technique, biological oxygen demand and total suspended solids are effectively reduced. Land availability is one main limiting factor in the development of constructed wetlands, especially in regions where land resources are scarce or there is high population density. Design, operation, technical guidance, and maintenance are the factors to be considered in improving the sustainability of constructed wetlands. Further, new studies are required to gain long-term operational data, which in turn is helpful in the successful application of constructed wetlands for treating wastewaters.