This article analyses corporate income taxation in Portugal. It provides an encompassing description of the Portuguese corporate income tax system. In addition, firm-level effective tax rates (ETR) are computed using a micro database, and their relation with several firms’ characteristics is examined in the period 2010-2019. In terms of results, Portugal stands out as one of the countries with higher top statutory tax rates amongst OECD countries. Although the general rate was cut over time, progressivity increased substantially and collection is very concentrated on a small number of large firms. Regression estimates suggest the existence of nonlinear relations between firms’ effective taxation and their size and productivity, and negative associations between ETR and both financial leverage and capital intensity.