Zero Liquid Discharge (ZLD) wastewater treatment systems represent a cutting-edge approach to sustainable water management. This chapter provides a comprehensive overview of ZLD systems, from their fundamental principles to practical applications, highlighting their environmental and economic benefits. The chapter begins by introducing the concept of ZLD, which aims to eliminate liquid waste by recovering and reusing all wastewater within an industrial process. It outlines the key components of ZLD systems, including advanced filtration, evaporation, and crystallization technologies. The discussion emphasizes the importance of ZLD in addressing water scarcity, regulatory compliance, and pollution control. Key areas of focus include the technical aspects of designing and implementing ZLD systems, such as selecting appropriate technologies, optimizing energy efficiency, and managing operational challenges. The chapter also explores the economic considerations, including the initial investment, operational costs, and potential financial returns through water reuse and resource recovery. Case studies from various industries, such as power generation, textiles, and pharmaceuticals, illustrate successful ZLD implementations and their positive environmental impact. By examining these real-world examples, the chapter highlights best practices and lessons learned. This chapter aims to provide stakeholders with a thorough understanding of ZLD systems, demonstrating their potential to achieve sustainable water management and environmental protection while also offering economic advantages. © 2025 Elsevier B.V., All rights reserved.