This collection brings together important contributions by leading econometricians on parametric approaches to qualitative and sample selection models, nonparametric and semi-parametric approaches to qualitative and sample selection models, and nonlinear estimation of cross-sectional and time series models. The advances achieved here can have important bearing on the choice of methods and analytical techniques in applied research. The collection of papers is dedicated to Professor Takeshi Amemiya in view of his path-breaking contributions to econometrics and statistics.