Principles of Econometrics, 4th Edition, is an introductory book on economics and finance designed to provide an understanding of why econometrics is necessary, and a working knowledge of basic econometric tools. This latest edition is updated to reflect current state of economic and financial markets and provides new content on Kernel Density Fitting and Analysis of Treatment Effects. It offers new end-of-chapters questions and problems in each chapter; updated comprehensive Glossary of Terms; and summary of Probably and Statistics. The text applies basic econometric tools to modeling, estimation, inference, and forecasting through real world problems and evaluates critically the results and conclusions from others who use basic econometric tools. Furthermore, it provides a foundation and understanding for further study of econometrics and more advanced techniques.