The present chapter focuses on the day fine model in Portugal. Based on an analysis of the historical development, the legal framework, the practical implementation and the public perception of the Portuguese day fines system, as well as of its constitutionality challenges, we conclude that, for the past two decades and although several other alternatives to imprisonment can be imposed, the day fine became the most frequently applied criminal sanction in Portugal, both as a primary and a substitutive penalty. We argue, however, that, in spite of the legal fairness of the adopted day fines regime and of the general level of acceptance of the day fine among the Portuguese courts and academic literature, the day fine has prima facie a retributive quality and, because of its maximum limits, hasn’t proved preventively adequate in the most economically lucrative offences (financial, environmental or political criminality), related to the offender’s cost-benefit equation. Furthermore, the subsidiary liability of corporate leaders for the fines imposed on legal persons raises difficult constitutionality issues.