Thesis: This thesis studies different aspects of firm dynamics both theoretically and empirically. All chapters extensively rely to large microeconomic dataset that are used to test theoretical predictions.First chapter looks at the innovation premium, that is the response to workers’ wage when their firm increases its R&D intensity and therefore becomes closer to the technological frontier. This response is evaluated using matched employers-employees data with information on the wage of 1% of all UK based workers. Second chapter focuses on the response to an export demand shock to a firm’s innovation and productivity looking at all French firms with at least one patent and using both fiscal and customs micro data. Finally, the third chapter considers the role of factor adjustment costs, especially on corporate real-estate, on firms employment dynamism following a productivity shock. This chapter uses a large sample of single-establishment French firms. Taken together, these three chapters explore different dimension of the response to firms to a demand and/or a productivity shock, either in terms of employment and wage, or in terms of innovation and size.