Since the 1990s casual workers in Argentina – defined as those who do not have access to social coverage – account for between 30% and 40% of the active population. The hardest hit are domestic workers (85%), rural workers (75%) and self-employed or independent workers (60%). The monotribut system is an innovative measure aimed at integrating low-income workers (salaried or independent) into the tax and social welfare system. It also aims at simplifying the registration process for these workers who have limited contributive capacity. This will be done by introducing a new tax combining income tax and Social Security charges (illness and pension). This article will analyse the consequences of this monotribut regime – as an institutional innovation – on the welfare system as a whole. What innovation does this new system bring compared to the current Bismarkian model ? Does this innovation call the structure of the general system into question ? If this is the case, is it a sign of a transition towards a new system ? Or is it simply a transformation to the current one ?