Tertiary treatment is a crucial phase in the overall process of municipal wastewater treatment or sewage treatment plants. It aims to remove residual contaminants that persist after primary and secondary treatment processes. This chapter provides a comprehensive analysis of tertiary treatment, including its objectives, methods, and operational considerations. By emphasizing the significance of tertiary treatment in meeting stringent water quality standards, this chapter aims to enhance understanding and facilitate the effective implementation of tertiary treatment strategies in municipal wastewater treatment systems.