With growing global water scarcity and rising awareness of wastewater’s potential value, the transition from linear “take-make-dispose” models to circular economy (CE) approaches in wastewater and sludge management is converting waste streams into valuable resources while addressing the complexities of global water scarcity and nutrient depletion. This chapter outlines the application of CE principles (reduce, reuse, recycle, and recovery) to redesign conventional wastewater treatment plants (WWTPs) into water resource recovery facilities (WRRFs) that recover water, energy, and nutrients. CE models are presented in a matrix framework to highlight circularity prospects at both liquid and solid treatment phases. Economic analyses show that CE models can reduce operating expenditure and create value through biogas, fertilizer, and reclaimed water. Aerobic granular sludge systems, anaerobic membrane bioreactors, and thermal technologies such as hydrothermal carbonization are important technologies for transitioning from WWTPs to WRRFs. Nutrient recovery, particularly phosphorus via struvite precipitation and membrane separations, has the potential to deliver significant economic and environmental benefits. But current challenges are still found in high capital cost, low elimination of emerging contaminants, and outdated policies. Economic viability is generally a function of scale, and this will dictate technology choice. Global studies demonstrate that effective CE implementation deserves stakeholder engagement, favorable policies, and context-specific technology implementation. It is summed up in the conclusion that regulatory, financial, and technological barriers could only be overcome with collaborative efforts, innovation, and uniform sustainability indicators. Effective CE practice could hugely increase resource recovery, minimize environmental footprint, and enhance water and nutrient security.