This paper carries out an empirical assessment of the relationship between social capital and labour productivity in small and medium enterprises in Italy. By means of structural equations models, the analysis investigates the effect of different aspects of the multifaceted concept of social capital. The bonding social capital of strong family ties and the bridging social capital shaped by informal ties connecting friends and acquaintances are proved to exert a negative effect on labour productivity, the economic performance, and human development. On the contrary, the linking social capital of voluntary organizations positively influences such outcomes.