The article discusses the principal factors that explain variations in trade union membership and number of working days lost due to strikes in Italy between 1960 and 1999. The econometric model presented shows the connections between the industrial relations system and the economic system. The relationship is bi-directional. The industrial relations variables that exert effects on the economy through prices and wages are in their turn affected by the economy: both by the trend in the economic cycle (the industrial production index which principally determines unionisation) and unemployment (which exerts its main negative effect on the strike rate). These economic variables influence a system whose functioning also displays margins of autonomy, which are particularly visible in the reciprocal determination at different times between strikes and unionisation. Today, however, the influence exerted by the volume of strikes on unionisation has diminished. The (positive sign) relation between strikes and unionisation continues to operate, but the decline in the former renders their influence on unionisation almost negligible in practical terms. The result is that the industrial relations system has less autonomy.