Physical organic chemistry – the study of the interplay between structure and reactivity in organic molecules – underpins organic chemistry, which cannot be imagined as a subject without knowledge of mechanism and reactivity. Applications to complex reactions in biology, polymer chemistry and electronic materials are ever more prevalent, and add to contributions in ‘small molecule’ chemistry. Novel experimental techniques combined with the revolution in computational chemistry give new impetus to physical organic chemistry and contribute to its continuing importance, which is reflected in the large number of international meetings in physical organic chemistry in the past two years.