Using transactions-level customs data from Colombia, we study firm-specific export patterns over the period 1996-2005. Our data allow us to track firms' entry and exit into and out of individual destination markets, as well as their revenues from selling there. We find that, in a typical year, nearly half of all Colombian exporters were not exporters in the previous year. These new exporters tend to be extremely small in terms of their overall contribution to export revenues, and most do not continue exporting in the following year. Hence export sales are dominated by a small number of very large and stable exporters. Nonetheless, out of each cohort of new exporters, a fraction of firms go on to expand their foreign sales very rapidly, and over the period of less than a decade, these successful new exporters account for almost half of total export expansion. Finally, we find that new exporters begin in a single foreign market and, if they survive, gradually expand into additional destinations. The geographic expansion paths they follow, and their likelihood of survival as exporters, depend on their initial destination market.