The increase in the consumption of ultra-processed foods (UPF) is negatively affecting public health at the global level. The UPF industry is a key driver of this trend, as its leading corporations and co-dependent actors have expanded and restructured food systems almost everywhere in the world. This development supports the spread of ultra-processed food. Political responses to this problem are emerging in a similar way to tobacco control in the past. A better understanding of the commercial determinants and root causes of the spread of UPF is needed. The goal is to accelerate global action and mobilize a public health response. This paper is the third in a three-part Lancet series to expand knowledge about the causes and inform the global response.