This Chapter addresses the crucial processes of preliminary and primary wastewater treatment, focusing on the removal of coarse solids and preparation for advanced treatment stages. It begins with an overview of initial therapy, highlighting operations like screening and filtering, and detailing components such as bar screens, fine screens, grit chambers, and comminutors. Flow equalization is also key to maintaining consistent hydraulic and organic loading. The chapter then covers coagulation and flocculation, explaining the mechanisms, chemical agents used, and design considerations for optimizing performance. It introduces Chemically Enhanced Primary Treatment to improve pollutant removal efficiency. The latter sections explore primary sedimentation, including settling phenomena, sedimentation theory, and tank design. It also touches on advanced topics like equations for settling velocity and using Computational Fluid Dynamics in design. Overall, this chapter provides essential knowledge and practical insights into the initial stages of wastewater treatment, setting the stage for secondary and tertiary strategies.