Two-stage least squares (TSLS) is a special case of instrumental variables regression. As the name Suggests, there are two distinct stages in the two-stage least squares. In the first stage, TSLS finds the portions of the endogenous and exogenous variables that can be Attributed to the instruments. This stage Estimating Involves an OLS regression of each variable in the models on the set of instruments. The second stage is a regression of the original equation, with all of the variables replaced by the fitted values from the first-stage regressions. The coefficients of this regression are the TSLS estimates. This tutorial Using Eviews 9 (Estimating TSLS in EViews 9)