This paper examines the impact of public capital on private sector productivity in Spain. Our analysis has been guided by the modern growth models, which have shown that there is indeed a positive influence of R&D and human capital investments on output growth, by contrast with traditional models with exogenous technical progress. The main result is that public activities such as the provision of infrastructures, investment in R&D and public expenditure on education, are relevant factors to explain economic growth. However, the impact of public capital decreases significantly when we incorporate other public activities.

Key words: economic growth, productivity, public capital, human capital, tecnological capital, Spain.
JEL Classification: D24, H52, H54, O32, O47.