In recent years, econometricians extended instrumental variable models, a standard approach to regression with endogeneity, to non/semi-parametric settings. However, when the endogenous variables are continuous, such models are exposed to ill-posed problems. Working from a different assumption, this book considers estimation of non/semi-parametric instrumental variables models under a functional coefficient form. Under this representation, models are linear in the endogenous components with either constant or unknown functional coefficients. Due to the linearity, the models avoid the...