This article describes the user-written command iop to estimate ex-ante inequality of opportunity for different types of variables. Inequality of opportunity is the part of inequality that is due to circumstances beyond the control of the individual. Therefore, it is the ethically offensive part of inequality. Several estimation procedures have been proposed over the past years, and iop is a comprehensive and easy-to-use command that implements many of them. It handles continuous, dichotomous, and ordered variables. In addition to the point estimates, iop also provides bootstrap standard errors and two decomposition methods.