Book section: This chapter draws on yearly data for the period 2000-09 relating to individual French exporters to analyse the changes in France's overall export value in response to demand shocks and to shed light on the debate surrounding trade elasticities. Over the medium term, two-thirds of the increase in overall exports witnessed during the observation period was accounted for by an expansion in existing trade flows, thereby leaving scope for new flows. Over the very short term, by contrast, trade flows adjust mainly at the intensive margin to large swings in demand. All this underlines the potential role of sunk costs, which introduce irreversibility into export decisions.