The ‘Wastewater treatment solutions for climate mitigation: a practical guide’ serves as a comprehensive resource for wastewater practitioners, policymakers, and researchers aiming to reduce greenhouse gas emissions in the sanitation sector. With wastewater treatment contributing up to a level of global emissions comparable to aviation and cement production, this timely guide emphasizes the urgent need to align sanitation goals with climate action. The technical guide provides detailed methodologies for monitoring and quantifying emissions, explores mitigation strategies through planning and process optimization, and highlights policy instruments and technologies that support the transition to net-zero wastewater treatment.This guide is a collaboration between UNEP, UNEP-DHI and the Global Wastewater Initiative.