This dissertation presents the results of an empirical investigation into the nature, causes and consequences of the export activity from the point of view of the firm. It comprises five essays, analysing the following topics: Chapter 1 investigates the dynamics of export behaviour among British small and medium sized firms (SMEs) in the nineties. We develop a dynamic model of entry decision in a foreign market that takes into account both unobserved firm heterogeneity and genuine state dependence. After controlling for unobservable firm heterogeneity, we find that up to 75 percent of export persistence in the data is explained by "true" state dependence, and that this dependence is greater among old companies than young companies. Moreover, observable firm characteristics such as size and ownership play a significant role in distinguishing exporters from non-exporters. Chapter 2 reports the results of an empirical investigation of the determinants of export diversification among Spanish exporters. The lack of theory, the unclear past empirical evidence and the use of the census of Spanish exporting firms justifies the use of semi-parametric regression techniques to characterise the pattern of export diversification as a firm becomes more internationalised. Unlike other studies, the finding suggests that the success of strong export-orientated firms relies heavily on both product and market specialisation. Chapter 3 analyses the role of information spillovers in the export destination decision by SMEs. With uncertainty and sunk entry costs, small firms will tend to export to countries where other local exporters have previous experience as information is cheaper and more reliable. In our application for Spain, the findings suggest that geographical agglomeration of exporting firms of the same industry selling to one destination significantly affects the probability of small-medium sized firms exporting to the same destination. The probability to export to one particular destination is also (positively) affected by firm characteristics such as size and export intensity, and gravitational factors such as the level of development and the physical proximity of the destination country. Chapter 4 examines the measurement of market power in an international duopoly market, the ceramic tile industry, over the period 1988-1998. After estimating the marginal costs of each competitor export group, we use both cross-section and time- series techniques to evaluate the degree of competition in this industry. The results suggest that Italian producers are ''leaders" and Spanish producers are ''followers" in a market characterised by substantial positive Chapter 5 investigates the relationship between export activity and technical efficiency using a large panel of firms in the UK manufacturing industry during the nineties. The findings show a positive impact of export status on long-run efficiency among those industries in which the UK reveals a comparative disadvantage, suggesting the important role played by firm competitiveness to overcome industry comparative disadvantage factors. In our analysis of short run efficiency changes, we do not find evidence that efficiency improves as firms become export dependent, markups