There is a growing need for cost-effective and more efficient alternative options for wastewater treatment. Green technologies continually evolve to offer sustainable solutions to modern societies’ growing and intensifying challenges. Constructed wetlands (CWs) are low-cost engineered systems for treating wastewater with proven treatment efficiency. The efficiency of CWs depends upon many factors, including the types of CWs, vegetation, hydraulic load, and the media utilized in the bed. This chapter will explore a wide range of CWs, including different types based on hydrology, macrophytic growth type, and water flow direction. It aims to highlight the applications of CWs and the recent innovations in CW technology like thermal insulation, bioengineering, reed box, the role of substrates, and the methods of improving the removal efficiency of CWs. This chapter indicates that major advances in the technology design, operation, and optimization of CWs using different mechanisms promote more sustainable, eco-friendly techniques for wastewater treatment.