This deliverable establishes the baseline framework for embedding sustainability into 6G networks, addressing both "Sustainable 6G" and "6G for Sustainability" aspects. It defines environmental, societal, and economic sustainability pillars and introduces key design principles, trade-offs, and evaluation metrics. A state-of-the-art review of enabling technologies and eco-design strategies is provided. The document also outlines -driven requirements derived from nine use cases across agriculture, smart grid, and telemedicine sectors. This foundation will guide technical development, system-level integration, and future validation within SUSTAIN-6G.