There are 2.4 billion people without improved sanitation and another 2.1 billion with inadequate sanitation (i.e. wastewater drains directly into surface waters), and despite improvements over the past decades, the unsafe management of fecal waste and wastewater continues to present a major risk to public health and the environment (UN, 2016). There is growing interest in low cost sanitation solutions which harness natural systems. However, it can be difficult for wastewater utility managers to understand under what conditions such nature-based solutions (NBS) might be applicable and how best to combine traditional infrastructure, for example an activated sludge treatment plant, with an NBS such as treatment wetlands. There is increasing scientific evidence that treatment systems with designs inspired by nature are highly efficient treatment technologies. The cost-effective design and implementation of ecosystems in wastewater treatment is something that exists and has the potential to be further promoted globally as both a sustainable and practical solution. This book serves as a compilation of technical references, case examples and guidance for applying nature-based solutions for treatment of domestic wastewater, and enables a wide variety of stakeholders to understand the design parameters, removal efficiencies, costs, co-benefits for both people and nature and trade-offs for consideration in their local context. Examples through case studies are from across the globe and provide practical insights into the variety of potentially applicable solutions.