This paper provides a synthesis of what is known about the determinants of output growth based on studying microeconomic data sets. It starts with a summary of the theoretical explanations which help reconcile heterogeneous performance observed across establishments in the same sector. The related theoretical literature on creative destruction models of growth is also discussed. This is followed by a review of the recent empirical literature on the relationship between microeconomic and macroeconomic productivity growth. The final section discusses the main empirical findings, the caveats of interpretation and the main issues of interpretation underlying the relationship between reallocation and growth ...