Dr Jonathan Cullen is the University Lecturer in Energy, Transport and Urban Infrastructure at the University of Cambridge. He leads the Resource Efficiency Collective (www.refficiency.org) and has a reputation for top-down studies of resource systems, bringing skills in developing new metrics to reflect both energy and material consequences of materials production. Jonathan studied Chemical and Process Engineering in New Zealand and began his career as a Process Engineer in heavy industry. After 5 years, he moved to Lima, Peru, where he was involved in projects with ITDG (Intermediate Technology Development Group) and UNALM (Universidad Nacional Agraria de La Molina) to develop biodiesel energy source options for Peru, including a mid-size plant to process used cooking oil in Lima and small-scale conversion of jungle seeds to biodiesel in isolated Amazon jungle communities. He also contracted Glidepath and Bechtel Overseas to design and install baggage handling and x-ray screening equipment at Lima and Santiago International Airports. After 10 years in industry and development work he moved to Cambridge to undertake the MPhil in Engineering for Sustainable Development and complete a PhD on the Engineering Fundamentals of Energy Efficiency, before taking up roles of Research Associate and then University Lecturer. Jonathan currently leads C-THRU: carbon clarity in the global petrochemical supply chain (VKRF, US$4m). He is currently a co-investigator on: S2uPPlant: Smart Sustainable Plastic Packaging from Plants (UKRI, £1m), UK FIRES: Locating Resource Efficiency at the heart of Future Industrial Strategy (EPSRC, £5.2m), and CirPlas: Circular Economy Approaches to Eliminate Plastic Waste (UKRI, £1.25m). He is a Lead Author for the IPCC AR6 Industry Chapter, an Expert Adviser to the IEA Technology Roadmaps, and co-authored the book Sustainable Materials: with both eyes open, which pioneered the concept of material efficiency for energy-intensive industries.