We modeled the carbon (C) cycle in Mexico with a process-based approach. We used different available products (satellite data, field measurements, models and flux towers) to estimate C stocks and fluxes in the country at three different time frames: present (defined as the period 2000-2005), the past century (1901-2000) and the remainder of this century (2010-2100). Our estimate of the gross primary productivity (GPP) for the country was 2137 +/- 1023 TgC yr(-1) and a total C stock of 34 506 +/- 7483 TgC, with 20 347 +/- 4622 TgC in vegetation and 14 159 +/- 3861 in the soil. Contrary to other current estimates for recent decades, our results showed that Mexico was a C sink over the period 1990-2009 (C 31 TgC yr(-1) ) and that C accumulation over the last century amounted to 1210 +/- 1040 TgC. We attributed this sink to the CO2 fertilization effect on GPP, which led to an increase of 3408 +/- 1060 TgC, while both climate and land use reduced the country C stocks by -458 +/- 1001 and -1740 +/- 878 TgC, respectively. Under different future scenarios, the C sink will likely continue over the 21st century, with decreasing C uptake as the climate forcing becomes more extreme. Our work provides valuable insights on relevant driving processes of the C cycle such as the role of drought in drylands (e.g., grasslands and shrublands) and the impact of climate change on the mean residence time of soil C in tropical ecosystems.