<p>The Planta paper “Some relationships between the biochemistry of photosynthesis and the gas exchange of leaves” explored the relationship between gas exchange measurements of CO₂ assimilation rate and the in vitro activity of Rubisco and chloroplast electron transport capacity. It showed that <i>A</i>/<i>C</i>_i curves, the response of CO₂ assimilation rate, <i>A</i>, to intercellular CO₂ partial pressure, <i>C</i>_<i>i</i>, were an ideal tool to capture the underlying photosynthetic biochemistry and could be used to quantify maximum Rubisco activity and electron transport capacity in vivo. We also derived the equations required to calculate <i>C</i>_<i>i</i> using a ternary diffusion model which are now used world-wide in portable gas exchange systems. Below we highlight the major findings reported in this paper and how they continue to influence current research.</p>