New technologies for recycling and waste valorisation 40 are required for chemistry to enter a circular economy, so that waste is valued as a resource. Such actions are necessary to slow land clearing and extraction of finite metal and petroleum feedstocks from fragile ecosystems. Where possible, "nexus" strategies should be used in which multiple challenges in sustainability are addressed at the same time. Conversion of waste CO2 into valuable chemicals, for instance, could potentially mitigate its harm as a greenhouse gas and provide valuable materials. Using industrial by-products as reagents to make materials that capture pollution addresses waste valorisation, environmental protection, and restoration. Similarly, using discarded plastic and tyres in the production of "Green Steel" repurposes waste and lowers the energy consumption in the manufacture of construction materials. More advances in this spirit are required for a sustainable built environment. For the manufacture of fine chemicals and pharmaceuticals, disruptive strategies are needed to reduce energy input and waste. Catalysis will play a central role in the future of Green Chemistry, with significant scope for biocatalysis. Enzymes, for instance, can orchestrate complex series of chemical reactions that are otherwise difficult to do with traditional non-biological chemistry. Enzymatic synthesis therefore has the potential to drastically reduce the number of steps and waste in a chemical manufacturing process. Advances in Green Chemistry and Engineering must also support the urgent and necessary transition to clean and sustainable energy. This responsibility spans improvements in the efficiency and sustainability of existing energy generation and storage technologies, 8 and the invention of new strategies for low-cost and recyclable solar harvesting systems and batteries. There is also an important role to play for Green Chemistry and Engineering in developing sustainable, zero-emission energy carriers such as hydrogen. These technologies are particularly important for the future of energy-intensive industries that are challenging to electrify, such as aviation 59 or steel production. It is not an overstatement to say that ensuring sustainable energy production, storage and use is one of the most important challenges we face as scientists and citizens. Green chemists and engineers are needed to deploy renewable energy broadly in society, and to use this energy to power the new chemistry, materials and technologies that support our well-being. In this way, reflecting on and adhering to the principles of Green Chemistry and Engineering is critical for our future.