Constructed wetlands (CWs) represent a sustainable and eco-friendly solution for wastewater treatment, effectively removing pollutants from various sources, including municipal wastewater, petroleum refinery effluent, agricultural runoff, and acid mine drainage. Over the past decade, advancements in microbiology have driven significant innovations in CW technology. This chapter provides an in-depth analysis of CWs, covering their types, contaminant removal mechanisms, degradation pathways, materials, applications, and the associated challenges and opportunities. It highlights the progress made over the last 30 years and explores unresolved issues, offering insights into potential future developments. By emphasizing innovative technologies, emerging trends, and research directions, this chapter serves as a valuable resource for the continued advancement of CWs.