Cotton (Gossypium hirsutum L.) is grown commercially in temperatures that vary greatly during the season. Understanding response patterns of leaf and internode expansion and duration of growth to temperature is essential to building a process-level crop simulation model. Such a model would be useful to aid in-season strategic management decisions. Plants were grown in sunlit plant growth chambers in five temperatures, 20/12°C to 40/32°C (day/night), at ambient (350 ml l-1 CO2) and twice ambient carbon dioxide levels in well watered and fertilized conditions. Plants were monitored daily for leaf unfolding dates, areas of leaves, and lengths of internodes at leaf unfolding, and growth of leaves and internodes. Durations of leaf and internode expansion were also determined. Leaf unfolding interval rates of both mainstem and fruiting branches increased as temperature increased; the rate of mainstem leaf unfolding interval increased more than the rate of branch leaf unfolding. Irrespective of sizes, leaves and internodes fit a single relationship of relative expansion rates and age for each temperature condition. Enriching CO2 to twice the ambient level did not change these relationships. Increasing temperature increased maximum growth rate, decreased the decay in the rate of expansion due to age, and reduced growth duration of both leaves and internodes. Internodes typically took less time than leaves to elongate at all temperatures. Leaf area and internode length at leaf unfolding increased as temperature increased to 27°C to 30°C, then decreased at higher temperatures. Leaf area at unfolding increased with mainstem node number until the plants started producing squares, about node 5, and produced smaller leaves thereafter. Internode lengths at leaf unfolding also increased as position on the mainstem increased until the plants started producing fruit, about node 15, and produced progressively shorter internode lengths at higher node positions. The relationships between temperature and rate functions such as leaf unfolding interval rates, maximum rate of growth, rate of decay with age, and expansion duration rate combined with leaf and internode sizes at leaf unfolding provide the necessary functional parameters to build process-level simulation models.