The document describes a linear model with endogenous regressors where yi=xi+ei and xi=zi+ui. It has an instrumental variable zi that satisfies the relevance condition of E[ziei]=0 and the exogeneity condition E[ziui]=0. Using this instrumental variable, the document shows that the two stage least squares estimator (2SLS), which first estimates xi as xi=zi and then regresses yi on the predicted xi, produces estimates that are equivalent to the instrumental variables estimator (IV) which directly regresses yi on zi weighted by xi.