The imperative to address climate change is only escalating. Nuclear fusion – the process that powers the Sun – offers the potential for carbon-free, effectively limitless, continuous electricity, if only it can be harnessed here on Earth. The Royal Society Kavli Medal and Lecture 2019 given by Professor Ian Chapman. Professor Ian Chapman and his colleagues are working to make fusion power a reality, and with the advent of ITER, the largest science experiment humankind has ever undertaken, they hope to demonstrate fusion power on a commercial scale. The UK, as one of the world leaders in fusion, is embarking on the design of a compact fusion reactor to follow ITER which aims to drive down the scale and cost of fusion power, which Professor Chapman explained and explored during his prize lecture. Background image: Inside JET, currently the world’s largest fusion experiment. Credit Eurofusion