Additive manufacturing (AM), or 3D printing, has revolutionized production by enabling complex designs, localized manufacturing, and reduced material waste compared to traditional methods. However, its sustainability is challenged by energy-intensive processes, reliance on non-renewable materials, and limited recyclability. This review critically evaluates the sustainability of 3D printing through three pillars: sustainable materials, energy-efficient processes, and circular economy integration. Advances in bio-based and recycled materials, process optimization techniques, and strategies for closed-loop systems are analyzed. Key challenges, including material degradation, high energy demands, and lifecycle assessment gaps, are discussed alongside opportunities for innovation. Recommendations for future research and policy are proposed to position AM as a sustainable manufacturing paradigm.