Over the course of 15 years, between 1992 and 2007, Mexico carried out a major land titling program that handed out certificates over usage rights for more than 90% of its communally held land (ejidos). Importantly, formally specifying usage rights through certification can reduce ambiguity in claims to property. The long run impact of this program is analyzed using data from 1991 and 2007, focusing on the average length of time land holdings have been certified. In order to control for selection, the advantage of the program's peculiar implementation strategy is taken. Certification is believed to be increasing investment in land specific assets, access to credit and use of land markets. While these findings stand alone as measures of outcomes of an important land reform, they are viewed as evidence that greater specificity improves the coordination of production plans.