Keeping wastewater treatment plants running smoothly requires proper maintenance. This chapter explains why maintenance is important, the different types (like checking regularly and fixing problems), and how to plan for it effectively. We discuss the various parts of a treatment plant that need maintenance, from big machines to buildings and pipes. The chapter also explains how to create a maintenance schedule, keep track of spare parts, and document everything that's done. Different techniques are covered, like regular cleaning and checks, using tools to predict problems before they happen, and fixing things when they break. We also talk about the skills and training needed by the people who maintain the plants, and how to manage the costs involved. Challenges that can arise during maintenance, like equipment failures or unexpected events, are addressed along with solutions and best practices for continuous improvement. Ultimately, the chapter emphasizes the importance of a proactive and sustainable approach to keep wastewater treatment plants functioning efficiently and reliably.